The fs module provides an API for interacting with the file system in a\nmanner closely modeled around standard POSIX functions.
To use this module:
\nconst fs = require('fs');\nAll file system operations have synchronous and asynchronous forms.
\nThe asynchronous form always takes a completion callback as its last argument.\nThe arguments passed to the completion callback depend on the method, but the\nfirst argument is always reserved for an exception. If the operation was\ncompleted successfully, then the first argument will be null or undefined.
const fs = require('fs');\n\nfs.unlink('/tmp/hello', (err) => {\n if (err) throw err;\n console.log('successfully deleted /tmp/hello');\n});\nExceptions that occur using synchronous operations are thrown immediately and\nmay be handled using try/catch, or may be allowed to bubble up.
const fs = require('fs');\n\ntry {\n fs.unlinkSync('/tmp/hello');\n console.log('successfully deleted /tmp/hello');\n} catch (err) {\n // handle the error\n}\nNote that there is no guaranteed ordering when using asynchronous methods.\nSo the following is prone to error because the fs.stat() operation may\ncomplete before the fs.rename() operation.
fs.rename('/tmp/hello', '/tmp/world', (err) => {\n if (err) throw err;\n console.log('renamed complete');\n});\nfs.stat('/tmp/world', (err, stats) => {\n if (err) throw err;\n console.log(`stats: ${JSON.stringify(stats)}`);\n});\nTo correctly order the operations, move the fs.stat() call into the callback\nof the fs.rename() operation:
fs.rename('/tmp/hello', '/tmp/world', (err) => {\n if (err) throw err;\n fs.stat('/tmp/world', (err, stats) => {\n if (err) throw err;\n console.log(`stats: ${JSON.stringify(stats)}`);\n });\n});\nIn busy processes, the programmer is strongly encouraged to use the\nasynchronous versions of these calls. The synchronous versions will block\nthe entire process until they complete — halting all connections.
\nWhile it is not recommended, most fs functions allow the callback argument to\nbe omitted, in which case a default callback is used that rethrows errors. To\nget a trace to the original call site, set the NODE_DEBUG environment\nvariable:
Omitting the callback function on asynchronous fs functions is deprecated and\nmay result in an error being thrown in the future.
\n$ cat script.js\nfunction bad() {\n require('fs').readFile('/');\n}\nbad();\n\n$ env NODE_DEBUG=fs node script.js\nfs.js:88\n throw backtrace;\n ^\nError: EISDIR: illegal operation on a directory, read\n <stack trace.>\nMost fs operations accept filepaths that may be specified in the form of\na string, a Buffer, or a URL object using the file: protocol.
String form paths are interpreted as UTF-8 character sequences identifying\nthe absolute or relative filename. Relative paths will be resolved relative\nto the current working directory as specified by process.cwd().
Example using an absolute path on POSIX:
\nconst fs = require('fs');\n\nfs.open('/open/some/file.txt', 'r', (err, fd) => {\n if (err) throw err;\n fs.close(fd, (err) => {\n if (err) throw err;\n });\n});\nExample using a relative path on POSIX (relative to process.cwd()):
fs.open('file.txt', 'r', (err, fd) => {\n if (err) throw err;\n fs.close(fd, (err) => {\n if (err) throw err;\n });\n});\nPaths specified using a Buffer are useful primarily on certain POSIX\noperating systems that treat file paths as opaque byte sequences. On such\nsystems, it is possible for a single file path to contain sub-sequences that\nuse multiple character encodings. As with string paths, Buffer paths may\nbe relative or absolute:
Example using an absolute path on POSIX:
\nfs.open(Buffer.from('/open/some/file.txt'), 'r', (err, fd) => {\n if (err) throw err;\n fs.close(fd, (err) => {\n if (err) throw err;\n });\n});\nNote: On Windows Node.js follows the concept of per-drive working directory.\nThis behavior can be observed when using a drive path without a backslash. For\nexample fs.readdirSync('c:\\\\') can potentially return a different result than\nfs.readdirSync('c:'). For more information, see\nthis MSDN page.
For most fs module functions, the path or filename argument may be passed\nas a WHATWG URL object. Only URL objects using the file: protocol\nare supported.
const fs = require('fs');\nconst fileUrl = new URL('file:///tmp/hello');\n\nfs.readFileSync(fileUrl);\nfile: URLs are always absolute paths.
Using WHATWG URL objects might introduce platform-specific behaviors.
On Windows, file: URLs with a hostname convert to UNC paths, while file:\nURLs with drive letters convert to local absolute paths. file: URLs without a\nhostname nor a drive letter will result in a throw :
// On Windows :\n\n// - WHATWG file URLs with hostname convert to UNC path\n// file://hostname/p/a/t/h/file => \\\\hostname\\p\\a\\t\\h\\file\nfs.readFileSync(new URL('file://hostname/p/a/t/h/file'));\n\n// - WHATWG file URLs with drive letters convert to absolute path\n// file:///C:/tmp/hello => C:\\tmp\\hello\nfs.readFileSync(new URL('file:///C:/tmp/hello'));\n\n// - WHATWG file URLs without hostname must have a drive letters\nfs.readFileSync(new URL('file:///notdriveletter/p/a/t/h/file'));\nfs.readFileSync(new URL('file:///c/p/a/t/h/file'));\n// TypeError [ERR_INVALID_FILE_URL_PATH]: File URL path must be absolute\nfile: URLs with drive letters must use : as a separator just after\nthe drive letter. Using another separator will result in a throw.
On all other platforms, file: URLs with a hostname are unsupported and will\nresult in a throw:
// On other platforms:\n\n// - WHATWG file URLs with hostname are unsupported\n// file://hostname/p/a/t/h/file => throw!\nfs.readFileSync(new URL('file://hostname/p/a/t/h/file'));\n// TypeError [ERR_INVALID_FILE_URL_PATH]: must be absolute\n\n// - WHATWG file URLs convert to absolute path\n// file:///tmp/hello => /tmp/hello\nfs.readFileSync(new URL('file:///tmp/hello'));\nA file: URL having encoded slash characters will result in a throw on all\nplatforms:
// On Windows\nfs.readFileSync(new URL('file:///C:/p/a/t/h/%2F'));\nfs.readFileSync(new URL('file:///C:/p/a/t/h/%2f'));\n/* TypeError [ERR_INVALID_FILE_URL_PATH]: File URL path must not include encoded\n\\ or / characters */\n\n// On POSIX\nfs.readFileSync(new URL('file:///p/a/t/h/%2F'));\nfs.readFileSync(new URL('file:///p/a/t/h/%2f'));\n/* TypeError [ERR_INVALID_FILE_URL_PATH]: File URL path must not include encoded\n/ characters */\nOn Windows, file: URLs having encoded backslash will result in a throw:
// On Windows\nfs.readFileSync(new URL('file:///C:/path/%5C'));\nfs.readFileSync(new URL('file:///C:/path/%5c'));\n/* TypeError [ERR_INVALID_FILE_URL_PATH]: File URL path must not include encoded\n\\ or / characters */\nOn POSIX systems, for every process, the kernel maintains a table of currently\nopen files and resources. Each open file is assigned a simple numeric\nidentifier called a file descriptor. At the system-level, all file system\noperations use these file descriptors to identify and track each specific\nfile. Windows systems use a different but conceptually similar mechanism for\ntracking resources. To simplify things for users, Node.js abstracts away the\nspecific differences between operating systems and assigns all open files a\nnumeric file descriptor.
\nThe fs.open() method is used to allocate a new file descriptor. Once\nallocated, the file descriptor may be used to read data from, write data to,\nor request information about the file.
fs.open('/open/some/file.txt', 'r', (err, fd) => {\n if (err) throw err;\n fs.fstat(fd, (err, stat) => {\n if (err) throw err;\n // use stat\n\n // always close the file descriptor!\n fs.close(fd, (err) => {\n if (err) throw err;\n });\n });\n});\nMost operating systems limit the number of file descriptors that may be open\nat any given time so it is critical to close the descriptor when operations\nare completed. Failure to do so will result in a memory leak that will\neventually cause an application to crash.
\n", "type": "module", "displayName": "File Descriptors" }, { "textRaw": "Threadpool Usage", "name": "threadpool_usage", "desc": "Note that all file system APIs except fs.FSWatcher() and those that are\nexplicitly synchronous use libuv's threadpool, which can have surprising and\nnegative performance implications for some applications, see the\nUV_THREADPOOL_SIZE documentation for more information.
path {string|Buffer|URL}options {string|Object}encoding {string} Default: 'utf8'callback {Function}err {Error}resolvedPath {string|Buffer}Asynchronous realpath(3).
\nThe callback gets two arguments (err, resolvedPath).
Only paths that can be converted to UTF8 strings are supported.
\nThe optional options argument can be a string specifying an encoding, or an\nobject with an encoding property specifying the character encoding to use for\nthe path passed to the callback. If the encoding is set to 'buffer',\nthe path returned will be passed as a Buffer object.
On Linux, when Node.js is linked against musl libc, the procfs file system must\nbe mounted on /proc in order for this function to work. Glibc does not have\nthis restriction.
path {string|Buffer|URL}options {string|Object}encoding {string} Default: 'utf8'Synchronous realpath(3).
\nOnly paths that can be converted to UTF8 strings are supported.
\nThe optional options argument can be a string specifying an encoding, or an\nobject with an encoding property specifying the character encoding to use for\nthe path passed to the callback. If the encoding is set to 'buffer',\nthe path returned will be passed as a Buffer object.
On Linux, when Node.js is linked against musl libc, the procfs file system must\nbe mounted on /proc in order for this function to work. Glibc does not have\nthis restriction.
The fs/promises API provides an alternative set of asynchronous file system\nmethods that return Promise objects rather than using callbacks. The\nAPI is accessible via require('fs/promises').
A FileHandle object is a wrapper for a numeric file descriptor.\nInstances of FileHandle are distinct from numeric file descriptors\nin that, if the FileHandle is not explicitly closed using the\nfilehandle.close() method, they will automatically close the file descriptor\nand will emit a process warning, thereby helping to prevent memory leaks.
Instances of the FileHandle object are created internally by the\nfsPromises.open() method.
Unlike callback-based such as fs.fstat(), fs.fchown(), fs.fchmod(),\nfs.ftruncate(), fs.read(), and fs.write(), operations — all of which\nuse a simple numeric file descriptor, all fsPromises.* variations use the\nFileHandle class in order to help protect against accidental leaking of\nunclosed file descriptors after a Promise is resolved or rejected.
Asynchronously append data to this file, creating the file if it does not yet\nexist. data can be a string or a Buffer. The Promise will be\nresolved with no arguments upon success.
If options is a string, then it specifies the encoding.
The FileHandle must have been opened for appending.
Modifies the permissions on the file. The Promise is resolved with no\narguments upon success.
Changes the ownership of the file then resolves the Promise with no arguments\nupon success.
Closes the file descriptor.
\nasync function openAndClose() {\n let filehandle;\n try {\n filehandle = await fsPromises.open('thefile.txt', 'r');\n } finally {\n if (filehandle !== undefined)\n await filehandle.close();\n }\n}\nAsynchronous fdatasync(2). The Promise is resolved with no arguments upon\nsuccess.
Read data from the file.
\nbuffer is the buffer that the data will be written to.
offset is the offset in the buffer to start writing at.
length is an integer specifying the number of bytes to read.
position is an argument specifying where to begin reading from in the file.\nIf position is null, data will be read from the current file position,\nand the file position will be updated.\nIf position is an integer, the file position will remain unchanged.
Following successful read, the Promise is resolved with an object with a\nbytesRead property specifying the number of bytes read, and a buffer\nproperty that is a reference to the passed in buffer argument.
Asynchronously reads the entire contents of a file.
\nThe Promise is resolved with the contents of the file. If no encoding is\nspecified (using options.encoding), the data is returned as a Buffer\nobject. Otherwise, the data will be a string.
If options is a string, then it specifies the encoding.
When the path is a directory, the behavior of fsPromises.readFile() is\nplatform-specific. On macOS, Linux, and Windows, the promise will be rejected\nwith an error. On FreeBSD, a representation of the directory's contents will be\nreturned.
The FileHandle has to support reading.
Retrieves the fs.Stats for the file.
Asynchronous fsync(2). The Promise is resolved with no arguments upon\nsuccess.
Truncates the file then resolves the Promise with no arguments upon success.
If the file was larger than len bytes, only the first len bytes will be\nretained in the file.
For example, the following program retains only the first four bytes of the\nfile:
\nconsole.log(fs.readFileSync('temp.txt', 'utf8'));\n// Prints: Node.js\n\nasync function doTruncate() {\n const fd = await fsPromises.open('temp.txt', 'r+');\n await fsPromises.ftruncate(fd, 4);\n console.log(fs.readFileSync('temp.txt', 'utf8')); // Prints: Node\n}\n\ndoTruncate().catch(console.error);\nIf the file previously was shorter than len bytes, it is extended, and the\nextended part is filled with null bytes ('\\0'). For example,
console.log(fs.readFileSync('temp.txt', 'utf8'));\n// Prints: Node.js\n\nasync function doTruncate() {\n const fd = await fsPromises.open('temp.txt', 'r+');\n await fsPromises.ftruncate(fd, 10);\n console.log(fs.readFileSync('temp.txt', 'utf8')); // Prints Node.js\\0\\0\\0\n}\n\ndoTruncate().catch(console.error);\nThe last three bytes are null bytes ('\\0'), to compensate the over-truncation.
\n" }, { "textRaw": "filehandle.utimes(atime, mtime)", "type": "method", "name": "utimes", "meta": { "added": [ "REPLACEME" ], "changes": [] }, "signatures": [ { "return": { "textRaw": "Returns: {Promise} ", "name": "return", "type": "Promise" }, "params": [ { "textRaw": "`atime` {number|string|Date} ", "name": "atime", "type": "number|string|Date" }, { "textRaw": "`mtime` {number|string|Date}` ", "name": "mtime", "type": "number|string|Date", "desc": "`" } ] }, { "params": [ { "name": "atime" }, { "name": "mtime" } ] } ], "desc": "Change the file system timestamps of the object referenced by the FileHandle\nthen resolves the Promise with no arguments upon success.
This function does not work on AIX versions before 7.1, it will resolve the\nPromise with an error using code UV_ENOSYS.
Write buffer to the file.
The Promise is resolved with an object containing a bytesWritten property\nidentifying the number of bytes written, and a buffer property containing\na reference to the buffer written.
offset determines the part of the buffer to be written, and length is\nan integer specifying the number of bytes to write.
position refers to the offset from the beginning of the file where this data\nshould be written. If typeof position !== 'number', the data will be written\nat the current position. See pwrite(2).
It is unsafe to use filehandle.write() multiple times on the same file\nwithout waiting for the Promise to be resolved (or rejected). For this\nscenario, fs.createWriteStream is strongly recommended.
On Linux, positional writes do not work when the file is opened in append mode.\nThe kernel ignores the position argument and always appends the data to\nthe end of the file.
\n" }, { "textRaw": "filehandle.writeFile(data, options)", "type": "method", "name": "writeFile", "meta": { "added": [ "REPLACEME" ], "changes": [] }, "signatures": [ { "return": { "textRaw": "Returns: {Promise} ", "name": "return", "type": "Promise" }, "params": [ { "textRaw": "`data` {string|Buffer|Uint8Array} ", "name": "data", "type": "string|Buffer|Uint8Array" }, { "textRaw": "`options` {Object|string} ", "options": [ { "textRaw": "`encoding` {string|null} **Default:** `'utf8'` ", "name": "encoding", "type": "string|null", "default": "`'utf8'`" }, { "textRaw": "`mode` {integer} **Default:** `0o666` ", "name": "mode", "type": "integer", "default": "`0o666`" }, { "textRaw": "`flag` {string} **Default:** `'w'` ", "name": "flag", "type": "string", "default": "`'w'`" } ], "name": "options", "type": "Object|string" } ] }, { "params": [ { "name": "data" }, { "name": "options" } ] } ], "desc": "Asynchronously writes data to a file, replacing the file if it already exists.\ndata can be a string or a buffer. The Promise will be resolved with no\narguments upon success.
The encoding option is ignored if data is a buffer.
If options is a string, then it specifies the encoding.
The FileHandle has to support writing.
It is unsafe to use filehandle.writeFile() multiple times on the same file\nwithout waiting for the Promise to be resolved (or rejected).
Tests a user's permissions for the file or directory specified by path.\nThe mode argument is an optional integer that specifies the accessibility\nchecks to be performed. The following constants define the possible values of\nmode. It is possible to create a mask consisting of the bitwise OR of two or\nmore values (e.g. fs.constants.W_OK | fs.constants.R_OK).
fs.constants.F_OK - path is visible to the calling process. This is useful\nfor determining if a file exists, but says nothing about rwx permissions.\nDefault if no mode is specified.fs.constants.R_OK - path can be read by the calling process.fs.constants.W_OK - path can be written by the calling process.fs.constants.X_OK - path can be executed by the calling process. This has\nno effect on Windows (will behave like fs.constants.F_OK).If the accessibility check is successful, the Promise is resolved with no\nvalue. If any of the accessibility checks fail, the Promise is rejected\nwith an Error object. The following example checks if the file\n/etc/passwd can be read and written by the current process.
fsPromises.access('/etc/passwd', fs.constants.R_OK | fs.constants.W_OK)\n .then(() => console.log('can access'))\n .catch(() => console.error('cannot access'));\nUsing fsPromises.access() to check for the accessibility of a file before\ncalling fsPromises.open() is not recommended. Doing so introduces a race\ncondition, since other processes may change the file's state between the two\ncalls. Instead, user code should open/read/write the file directly and handle\nthe error raised if the file is not accessible.
Asynchronously append data to a file, creating the file if it does not yet\nexist. data can be a string or a Buffer. The Promise will be\nresolved with no arguments upon success.
If options is a string, then it specifies the encoding.
The file may be specified as a FileHandle that has been opened\nfor appending (using fsPromises.open()).
Changes the permissions of a file then resolves the Promise with no\narguments upon succces.
Changes the ownership of a file then resolves the Promise with no arguments\nupon success.
Asynchronously copies src to dest. By default, dest is overwritten if it\nalready exists. The Promise will be resolved with no arguments upon success.
Node.js makes no guarantees about the atomicity of the copy operation. If an\nerror occurs after the destination file has been opened for writing, Node.js\nwill attempt to remove the destination.
\nflags is an optional integer that specifies the behavior\nof the copy operation. It is possible to create a mask consisting of the bitwise\nOR of two or more values (e.g.\nfs.constants.COPYFILE_EXCL | fs.constants.COPYFILE_FICLONE).
fs.constants.COPYFILE_EXCL - The copy operation will fail if dest already\nexists.fs.constants.COPYFILE_FICLONE - The copy operation will attempt to create a\ncopy-on-write reflink. If the platform does not support copy-on-write, then a\nfallback copy mechanism is used.fs.constants.COPYFILE_FICLONE_FORCE - The copy operation will attempt to\ncreate a copy-on-write reflink. If the platform does not support copy-on-write,\nthen the operation will fail.Example:
\nconst fs = require('fs');\n\n// destination.txt will be created or overwritten by default.\nfsPromises.copyFile('source.txt', 'destination.txt')\n .then(() => console.log('source.txt was copied to destination.txt'))\n .catch(() => console.log('The file could not be copied'));\nIf the third argument is a number, then it specifies flags, as shown in the\nfollowing example.
const fs = require('fs');\nconst { COPYFILE_EXCL } = fs.constants;\n\n// By using COPYFILE_EXCL, the operation will fail if destination.txt exists.\nfsPromises.copyFile('source.txt', 'destination.txt', COPYFILE_EXCL)\n .then(() => console.log('source.txt was copied to destination.txt'))\n .catch(() => console.log('The file could not be copied'));\nAsynchronous fchmod(2). The Promise is resolved with no arguments upon\nsuccess.
Changes the ownership of the file represented by filehandle then resolves\nthe Promise with no arguments upon success.
Asynchronous fdatasync(2). The Promise is resolved with no arguments upon\nsuccess.
Retrieves the fs.Stats for the given filehandle.
Asynchronous fsync(2). The Promise is resolved with no arguments upon\nsuccess.
Truncates the file represented by filehandle then resolves the Promise\nwith no arguments upon success.
If the file referred to by the FileHandle was larger than len bytes, only\nthe first len bytes will be retained in the file.
For example, the following program retains only the first four bytes of the\nfile:
\nconsole.log(fs.readFileSync('temp.txt', 'utf8'));\n// Prints: Node.js\n\nasync function doTruncate() {\n const fd = await fsPromises.open('temp.txt', 'r+');\n await fsPromises.ftruncate(fd, 4);\n console.log(fs.readFileSync('temp.txt', 'utf8')); // Prints: Node\n}\n\ndoTruncate().catch(console.error);\nIf the file previously was shorter than len bytes, it is extended, and the\nextended part is filled with null bytes ('\\0'). For example,
console.log(fs.readFileSync('temp.txt', 'utf8'));\n// Prints: Node.js\n\nasync function doTruncate() {\n const fd = await fsPromises.open('temp.txt', 'r+');\n await fsPromises.ftruncate(fd, 10);\n console.log(fs.readFileSync('temp.txt', 'utf8')); // Prints Node.js\\0\\0\\0\n}\n\ndoTruncate().catch(console.error);\nThe last three bytes are null bytes ('\\0'), to compensate the over-truncation.
\n" }, { "textRaw": "fsPromises.futimes(filehandle, atime, mtime)", "type": "method", "name": "futimes", "meta": { "added": [ "REPLACEME" ], "changes": [] }, "signatures": [ { "return": { "textRaw": "Returns: {Promise} ", "name": "return", "type": "Promise" }, "params": [ { "textRaw": "`filehandle` {FileHandle} ", "name": "filehandle", "type": "FileHandle" }, { "textRaw": "`atime` {number|string|Date} ", "name": "atime", "type": "number|string|Date" }, { "textRaw": "`mtime` {number|string|Date}` ", "name": "mtime", "type": "number|string|Date", "desc": "`" } ] }, { "params": [ { "name": "filehandle" }, { "name": "atime" }, { "name": "mtime" } ] } ], "desc": "Change the file system timestamps of the object referenced by the supplied\nFileHandle then resolves the Promise with no arguments upon success.
This function does not work on AIX versions before 7.1, it will resolve the\nPromise with an error using code UV_ENOSYS.
Changes the permissions on a symbolic link then resolves the Promise with\nno arguments upon success. This method is only implemented on macOS.
Changes the ownership on a symbolic link then resolves the Promise with\nno arguments upon success. This method is only implemented on macOS.
Asynchronous link(2). The Promise is resolved with no arguments upon success.
Asynchronous lstat(2). The Promise is resolved with the fs.Stats object\nfor the given symbolic link path.
Asynchronously creates a directory then resolves the Promise with no\narguments upon success.
Creates a unique temporary directory then resolves the Promise with the\ncreated folder path. A unique directory name is generated by appending six\nrandom characters to the end of the provided prefix.
The optional options argument can be a string specifying an encoding, or an\nobject with an encoding property specifying the character encoding to use.
Example:
\nfsPromises.mkdtemp(path.join(os.tmpdir(), 'foo-'))\n .catch(console.error);\nThe fs.mkdtemp() method will append the six randomly selected characters\ndirectly to the prefix string. For instance, given a directory /tmp, if the\nintention is to create a temporary directory within /tmp, the prefix\nmust end with a trailing platform-specific path separator\n(require('path').sep).
Asynchronous file open that returns a Promise that, when resolved, yields a\nFileHandle object. See open(2).
The flags argument can be:
'r' - Open file for reading.\nAn exception occurs if the file does not exist.
'r+' - Open file for reading and writing.\nAn exception occurs if the file does not exist.
'rs+' - Open file for reading and writing in synchronous mode. Instructs\nthe operating system to bypass the local file system cache.
This is primarily useful for opening files on NFS mounts as it allows skipping\nthe potentially stale local cache. It has a very real impact on I/O\nperformance so using this flag is not recommended unless it is needed.
\nNote that this does not turn fsPromises.open() into a synchronous blocking\ncall.
'w' - Open file for writing.\nThe file is created (if it does not exist) or truncated (if it exists).
'wx' - Like 'w' but fails if path exists.
'w+' - Open file for reading and writing.\nThe file is created (if it does not exist) or truncated (if it exists).
'wx+' - Like 'w+' but fails if path exists.
'a' - Open file for appending.\nThe file is created if it does not exist.
'ax' - Like 'a' but fails if path exists.
'as' - Open file for appending in synchronous mode.\nThe file is created if it does not exist.
'a+' - Open file for reading and appending.\nThe file is created if it does not exist.
'ax+' - Like 'a+' but fails if path exists.
'as+' - Open file for reading and appending in synchronous mode.\nThe file is created if it does not exist.
mode sets the file mode (permission and sticky bits), but only if the file was\ncreated.
The exclusive flag 'x' (O_EXCL flag in open(2)) ensures that path is newly\ncreated. On POSIX systems, path is considered to exist even if it is a symlink\nto a non-existent file. The exclusive flag may or may not work with network file\nsystems.
flags can also be a number as documented by open(2); commonly used constants\nare available from fs.constants. On Windows, flags are translated to\ntheir equivalent ones where applicable, e.g. O_WRONLY to FILE_GENERIC_WRITE,\nor O_EXCL|O_CREAT to CREATE_NEW, as accepted by CreateFileW.
On Linux, positional writes don't work when the file is opened in append mode.\nThe kernel ignores the position argument and always appends the data to\nthe end of the file.
\nThe behavior of fsPromises.open() is platform-specific for some\nflags. As such, opening a directory on macOS and Linux with the 'a+' flag will\nreturn an error. In contrast, on Windows and FreeBSD, a FileHandle will be\nreturned.
Some characters (< > : " / \\ | ? *) are reserved under Windows as documented\nby Naming Files, Paths, and Namespaces. Under NTFS, if the filename contains\na colon, Node.js will open a file system stream, as described by\nthis MSDN page.
Note: On Windows, opening an existing hidden file using the w flag (e.g.\nusing fsPromises.open()) will fail with EPERM. Existing hidden\nfiles can be opened for writing with the r+ flag. A call to\nfsPromises.ftruncate() can be used to reset the file contents.
Read data from the file specified by filehandle.
buffer is the buffer that the data will be written to.
offset is the offset in the buffer to start writing at.
length is an integer specifying the number of bytes to read.
position is an argument specifying where to begin reading from in the file.\nIf position is null, data will be read from the current file position,\nand the file position will be updated.\nIf position is an integer, the file position will remain unchanged.
Following successful read, the Promise is resolved with an object with a\nbytesRead property specifying the number of bytes read, and a buffer\nproperty that is a reference to the passed in buffer argument.
Reads the contents of a directory then resolves the Promise with an array\nof the names of the files in the directory excludiing '.' and '..'.
The optional options argument can be a string specifying an encoding, or an\nobject with an encoding property specifying the character encoding to use for\nthe filenames. If the encoding is set to 'buffer', the filenames returned\nwill be passed as Buffer objects.
Asynchronously reads the entire contents of a file.
\nThe Promise is resolved with the contents of the file. If no encoding is\nspecified (using options.encoding), the data is returned as a Buffer\nobject. Otherwise, the data will be a string.
If options is a string, then it specifies the encoding.
When the path is a directory, the behavior of fsPromises.readFile() is\nplatform-specific. On macOS, Linux, and Windows, the promise will be rejected\nwith an error. On FreeBSD, a representation of the directory's contents will be\nreturned.
Any specified FileHandle has to support reading.
Asynchronous readlink(2). The Promise is resolved with the linkString upon\nsuccess.
The optional options argument can be a string specifying an encoding, or an\nobject with an encoding property specifying the character encoding to use for\nthe link path returned. If the encoding is set to 'buffer', the link path\nreturned will be passed as a Buffer object.
Determines the actual location of path using the same semantics as the\nfs.realpath.native() function then resolves the Promise with the resolved\npath.
Only paths that can be converted to UTF8 strings are supported.
\nThe optional options argument can be a string specifying an encoding, or an\nobject with an encoding property specifying the character encoding to use for\nthe path. If the encoding is set to 'buffer', the path returned will be\npassed as a Buffer object.
On Linux, when Node.js is linked against musl libc, the procfs file system must\nbe mounted on /proc in order for this function to work. Glibc does not have\nthis restriction.
Renames oldPath to newPath and resolves the Promise with no arguments\nupon success.
Removes the directory identified by path then resolves the Promise with\nno arguments upon success.
Using fsPromises.rmdir() on a file (not a directory) results in the\nPromise being rejected with an ENOENT error on Windows and an ENOTDIR\nerror on POSIX.
The Promise is resolved with the fs.Stats object for the given path.
Creates a symbolic link then resolves the Promise with no arguments upon\nsuccess.
The type argument is only used on Windows platforms and can be one of 'dir',\n'file', or 'junction'. Note that Windows junction\npoints require the destination path to be absolute. When using 'junction',\nthe target argument will automatically be normalized to absolute path.
Truncates the path then resolves the Promise with no arguments upon\nsuccess. The path must be a string or Buffer.
Asynchronous unlink(2). The Promise is resolved with no arguments upon\nsuccess.
Change the file system timestamps of the object referenced by path then\nresolves the Promise with no arguments upon success.
The atime and mtime arguments follow these rules:
Dates, or a\nnumeric string like '123456789.0'.NaN, Infinity or\n-Infinity, an Error will be thrown.Write buffer to the file specified by filehandle.
The Promise is resolved with an object containing a bytesWritten property\nidentifying the number of bytes written, and a buffer property containing\na reference to the buffer written.
offset determines the part of the buffer to be written, and length is\nan integer specifying the number of bytes to write.
position refers to the offset from the beginning of the file where this data\nshould be written. If typeof position !== 'number', the data will be written\nat the current position. See pwrite(2).
It is unsafe to use fsPromises.write() multiple times on the same file\nwithout waiting for the Promise to be resolved (or rejected). For this\nscenario, fs.createWriteStream is strongly recommended.
On Linux, positional writes do not work when the file is opened in append mode.\nThe kernel ignores the position argument and always appends the data to\nthe end of the file.
\n" }, { "textRaw": "fsPromises.writeFile(file, data[, options])", "type": "method", "name": "writeFile", "meta": { "added": [ "REPLACEME" ], "changes": [] }, "signatures": [ { "return": { "textRaw": "Returns: {Promise} ", "name": "return", "type": "Promise" }, "params": [ { "textRaw": "`file` {string|Buffer|URL|FileHandle} filename or `FileHandle` ", "name": "file", "type": "string|Buffer|URL|FileHandle", "desc": "filename or `FileHandle`" }, { "textRaw": "`data` {string|Buffer|Uint8Array} ", "name": "data", "type": "string|Buffer|Uint8Array" }, { "textRaw": "`options` {Object|string} ", "options": [ { "textRaw": "`encoding` {string|null} **Default:** `'utf8'` ", "name": "encoding", "type": "string|null", "default": "`'utf8'`" }, { "textRaw": "`mode` {integer} **Default:** `0o666` ", "name": "mode", "type": "integer", "default": "`0o666`" }, { "textRaw": "`flag` {string} **Default:** `'w'` ", "name": "flag", "type": "string", "default": "`'w'`" } ], "name": "options", "type": "Object|string", "optional": true } ] }, { "params": [ { "name": "file" }, { "name": "data" }, { "name": "options", "optional": true } ] } ], "desc": "Asynchronously writes data to a file, replacing the file if it already exists.\ndata can be a string or a buffer. The Promise will be resolved with no\narguments upon success.
The encoding option is ignored if data is a buffer.
If options is a string, then it specifies the encoding.
Any specified FileHandle has to support writing.
It is unsafe to use fsPromises.writeFile() multiple times on the same file\nwithout waiting for the Promise to be resolved (or rejected).
The following constants are exported by fs.constants.
Not every constant will be available on every operating system.
\n", "modules": [ { "textRaw": "File Access Constants", "name": "file_access_constants", "desc": "The following constants are meant for use with fs.access().
| Constant | \nDescription | \n
|---|---|
F_OK | \n Flag indicating that the file is visible to the calling process. | \n
R_OK | \n Flag indicating that the file can be read by the calling process. | \n
W_OK | \n Flag indicating that the file can be written by the calling\n process. | \n
X_OK | \n Flag indicating that the file can be executed by the calling\n process. | \n
The following constants are meant for use with fs.copyFile().
| Constant | \nDescription | \n
|---|---|
COPYFILE_EXCL | \n If present, the copy operation will fail with an error if the\n destination path already exists. | \n
COPYFILE_FICLONE | \n If present, the copy operation will attempt to create a\n copy-on-write reflink. If the underlying platform does not support\n copy-on-write, then a fallback copy mechanism is used. | \n
COPYFILE_FICLONE_FORCE | \n If present, the copy operation will attempt to create a\n copy-on-write reflink. If the underlying platform does not support\n copy-on-write, then the operation will fail with an error. | \n
The following constants are meant for use with fs.open().
| Constant | \nDescription | \n
|---|---|
O_RDONLY | \n Flag indicating to open a file for read-only access. | \n
O_WRONLY | \n Flag indicating to open a file for write-only access. | \n
O_RDWR | \n Flag indicating to open a file for read-write access. | \n
O_CREAT | \n Flag indicating to create the file if it does not already exist. | \n
O_EXCL | \n Flag indicating that opening a file should fail if the\n O_CREAT flag is set and the file already exists. | \n
O_NOCTTY | \n Flag indicating that if path identifies a terminal device, opening the\n path shall not cause that terminal to become the controlling terminal for\n the process (if the process does not already have one). | \n
O_TRUNC | \n Flag indicating that if the file exists and is a regular file, and the\n file is opened successfully for write access, its length shall be truncated\n to zero. | \n
O_APPEND | \n Flag indicating that data will be appended to the end of the file. | \n
O_DIRECTORY | \n Flag indicating that the open should fail if the path is not a\n directory. | \n
O_NOATIME | \n Flag indicating reading accesses to the file system will no longer\n result in an update to the atime information associated with the file.\n This flag is available on Linux operating systems only. | \n
O_NOFOLLOW | \n Flag indicating that the open should fail if the path is a symbolic\n link. | \n
O_SYNC | \n Flag indicating that the file is opened for synchronized I/O with write\n operations waiting for file integrity. | \n
O_DSYNC | \n Flag indicating that the file is opened for synchronized I/O with write\n operations waiting for data integrity. | \n
O_SYMLINK | \n Flag indicating to open the symbolic link itself rather than the\n resource it is pointing to. | \n
O_DIRECT | \n When set, an attempt will be made to minimize caching effects of file\n I/O. | \n
O_NONBLOCK | \n Flag indicating to open the file in nonblocking mode when possible. | \n
The following constants are meant for use with the fs.Stats object's\nmode property for determining a file's type.
| Constant | \nDescription | \n
|---|---|
S_IFMT | \n Bit mask used to extract the file type code. | \n
S_IFREG | \n File type constant for a regular file. | \n
S_IFDIR | \n File type constant for a directory. | \n
S_IFCHR | \n File type constant for a character-oriented device file. | \n
S_IFBLK | \n File type constant for a block-oriented device file. | \n
S_IFIFO | \n File type constant for a FIFO/pipe. | \n
S_IFLNK | \n File type constant for a symbolic link. | \n
S_IFSOCK | \n File type constant for a socket. | \n
The following constants are meant for use with the fs.Stats object's\nmode property for determining the access permissions for a file.
| Constant | \nDescription | \n
|---|---|
S_IRWXU | \n File mode indicating readable, writable, and executable by owner. | \n
S_IRUSR | \n File mode indicating readable by owner. | \n
S_IWUSR | \n File mode indicating writable by owner. | \n
S_IXUSR | \n File mode indicating executable by owner. | \n
S_IRWXG | \n File mode indicating readable, writable, and executable by group. | \n
S_IRGRP | \n File mode indicating readable by group. | \n
S_IWGRP | \n File mode indicating writable by group. | \n
S_IXGRP | \n File mode indicating executable by group. | \n
S_IRWXO | \n File mode indicating readable, writable, and executable by others. | \n
S_IROTH | \n File mode indicating readable by others. | \n
S_IWOTH | \n File mode indicating writable by others. | \n
S_IXOTH | \n File mode indicating executable by others. | \n
A successful call to fs.watch() method will return a new fs.FSWatcher\nobject.
All fs.FSWatcher objects are EventEmitter's that will emit a 'change'\nevent whenever a specific watched file is modified.
Emitted when something changes in a watched directory or file.\nSee more details in fs.watch().
The filename argument may not be provided depending on operating system\nsupport. If filename is provided, it will be provided as a Buffer if\nfs.watch() is called with its encoding option set to 'buffer', otherwise\nfilename will be a UTF-8 string.
// Example when handled through fs.watch() listener\nfs.watch('./tmp', { encoding: 'buffer' }, (eventType, filename) => {\n if (filename) {\n console.log(filename);\n // Prints: <Buffer ...>\n }\n});\nEmitted when the watcher stops watching for changes.
\n", "params": [] }, { "textRaw": "Event: 'error'", "type": "event", "name": "error", "meta": { "added": [ "v0.5.8" ], "changes": [] }, "params": [], "desc": "Emitted when an error occurs while watching the file.
\n" } ], "methods": [ { "textRaw": "watcher.close()", "type": "method", "name": "close", "meta": { "added": [ "v0.5.8" ], "changes": [] }, "desc": "Stop watching for changes on the given fs.FSWatcher. Once stopped, the\nfs.FSWatcher object is no longer usable.
A successful call to fs.createReadStream() will return a new fs.ReadStream\nobject.
All fs.ReadStream objects are Readable Streams.
Emitted when the fs.ReadStream's underlying file descriptor has been closed.
Emitted when the fs.ReadStream's file descriptor has been opened.
Emitted when the fs.ReadStream is ready to be used.
Fires immediately after 'open'.
The number of bytes that have been read so far.
\n" }, { "textRaw": "`path` {string|Buffer} ", "type": "string|Buffer", "name": "path", "meta": { "added": [ "v0.1.93" ], "changes": [] }, "desc": "The path to the file the stream is reading from as specified in the first\nargument to fs.createReadStream(). If path is passed as a string, then\nreadStream.path will be a string. If path is passed as a Buffer, then\nreadStream.path will be a Buffer.
A fs.Stats object provides information about a file.
Objects returned from fs.stat(), fs.lstat() and fs.fstat() and\ntheir synchronous counterparts are of this type.
Stats {\n dev: 2114,\n ino: 48064969,\n mode: 33188,\n nlink: 1,\n uid: 85,\n gid: 100,\n rdev: 0,\n size: 527,\n blksize: 4096,\n blocks: 8,\n atimeMs: 1318289051000.1,\n mtimeMs: 1318289051000.1,\n ctimeMs: 1318289051000.1,\n birthtimeMs: 1318289051000.1,\n atime: Mon, 10 Oct 2011 23:24:11 GMT,\n mtime: Mon, 10 Oct 2011 23:24:11 GMT,\n ctime: Mon, 10 Oct 2011 23:24:11 GMT,\n birthtime: Mon, 10 Oct 2011 23:24:11 GMT }\nReturns true if the fs.Stats object describes a block device.
Returns true if the fs.Stats object describes a character device.
Returns true if the fs.Stats object describes a file system directory.
Returns true if the fs.Stats object describes a first-in-first-out (FIFO)\npipe.
Returns true if the fs.Stats object describes a regular file.
Returns true if the fs.Stats object describes a socket.
Returns true if the fs.Stats object describes a symbolic link.
This method is only valid when using fs.lstat()
The numeric identifier of the device containing the file.
\n" }, { "textRaw": "`ino` {number} ", "type": "number", "name": "ino", "desc": "The file system specific "Inode" number for the file.
\n" }, { "textRaw": "`mode` {number} ", "type": "number", "name": "mode", "desc": "A bit-field describing the file type and mode.
\n" }, { "textRaw": "`nlink` {number} ", "type": "number", "name": "nlink", "desc": "The number of hard-links that exist for the file.
\n" }, { "textRaw": "`uid` {number} ", "type": "number", "name": "uid", "desc": "The numeric user identifier of the user that owns the file (POSIX).
\n" }, { "textRaw": "`gid` {number} ", "type": "number", "name": "gid", "desc": "The numeric group identifier of the group that owns the file (POSIX).
\n" }, { "textRaw": "`rdev` {number} ", "type": "number", "name": "rdev", "desc": "A numeric device identifier if the file is considered "special".
\n" }, { "textRaw": "`size` {number} ", "type": "number", "name": "size", "desc": "The size of the file in bytes.
\n" }, { "textRaw": "`blksize` {number} ", "type": "number", "name": "blksize", "desc": "The file system block size for i/o operations.
\n" }, { "textRaw": "`blocks` {number} ", "type": "number", "name": "blocks", "desc": "The number of blocks allocated for this file.
\n" }, { "textRaw": "`atimeMs` {number} ", "type": "number", "name": "atimeMs", "meta": { "added": [ "v8.1.0" ], "changes": [] }, "desc": "The timestamp indicating the last time this file was accessed expressed in\nmilliseconds since the POSIX Epoch.
\n" }, { "textRaw": "`mtimeMs` {number} ", "type": "number", "name": "mtimeMs", "meta": { "added": [ "v8.1.0" ], "changes": [] }, "desc": "The timestamp indicating the last time this file was modified expressed in\nmilliseconds since the POSIX Epoch.
\n" }, { "textRaw": "`ctimeMs` {number} ", "type": "number", "name": "ctimeMs", "meta": { "added": [ "v8.1.0" ], "changes": [] }, "desc": "The timestamp indicating the last time the file status was changed expressed\nin milliseconds since the POSIX Epoch.
\n" }, { "textRaw": "`birthtimeMs` {number} ", "type": "number", "name": "birthtimeMs", "meta": { "added": [ "v8.1.0" ], "changes": [] }, "desc": "The timestamp indicating the creation time of this file expressed in\nmilliseconds since the POSIX Epoch.
\n" }, { "textRaw": "`atime` {Date} ", "type": "Date", "name": "atime", "meta": { "added": [ "v0.11.13" ], "changes": [] }, "desc": "The timestamp indicating the last time this file was accessed.
\n" }, { "textRaw": "`mtime` {Date} ", "type": "Date", "name": "mtime", "meta": { "added": [ "v0.11.13" ], "changes": [] }, "desc": "The timestamp indicating the last time this file was modified.
\n" }, { "textRaw": "`ctime` {Date} ", "type": "Date", "name": "ctime", "meta": { "added": [ "v0.11.13" ], "changes": [] }, "desc": "The timestamp indicating the last time the file status was changed.
\n" }, { "textRaw": "`birthtime` {Date} ", "type": "Date", "name": "birthtime", "meta": { "added": [ "v0.11.13" ], "changes": [] }, "desc": "The timestamp indicating the creation time of this file.
\n" } ], "modules": [ { "textRaw": "Stat Time Values", "name": "stat_time_values", "desc": "The atimeMs, mtimeMs, ctimeMs, birthtimeMs properties are\nnumbers that hold the corresponding times in milliseconds. Their\nprecision is platform specific. atime, mtime, ctime, and birthtime are\nDate object alternate representations of the various times. The\nDate and number values are not connected. Assigning a new number value, or\nmutating the Date value, will not be reflected in the corresponding alternate\nrepresentation.
The times in the stat object have the following semantics:
\natime "Access Time" - Time when file data last accessed. Changed\nby the mknod(2), utimes(2), and read(2) system calls.mtime "Modified Time" - Time when file data last modified.\nChanged by the mknod(2), utimes(2), and write(2) system calls.ctime "Change Time" - Time when file status was last changed\n(inode data modification). Changed by the chmod(2), chown(2),\nlink(2), mknod(2), rename(2), unlink(2), utimes(2),\nread(2), and write(2) system calls.birthtime "Birth Time" - Time of file creation. Set once when the\nfile is created. On filesystems where birthtime is not available,\nthis field may instead hold either the ctime or\n1970-01-01T00:00Z (ie, unix epoch timestamp 0). Note that this\nvalue may be greater than atime or mtime in this case. On Darwin\nand other FreeBSD variants, also set if the atime is explicitly\nset to an earlier value than the current birthtime using the\nutimes(2) system call.Prior to Node.js v0.12, the ctime held the birthtime on Windows\nsystems. Note that as of v0.12, ctime is not "creation time", and\non Unix systems, it never was.
WriteStream is a Writable Stream.
Emitted when the WriteStream's underlying file descriptor has been closed.
Emitted when the WriteStream's file is opened.
Emitted when the fs.WriteStream is ready to be used.
Fires immediately after 'open'.
The number of bytes written so far. Does not include data that is still queued\nfor writing.
\n" }, { "textRaw": "writeStream.path", "name": "path", "meta": { "added": [ "v0.1.93" ], "changes": [] }, "desc": "The path to the file the stream is writing to as specified in the first\nargument to fs.createWriteStream(). If path is passed as a string, then\nwriteStream.path will be a string. If path is passed as a Buffer, then\nwriteStream.path will be a Buffer.
Tests a user's permissions for the file or directory specified by path.\nThe mode argument is an optional integer that specifies the accessibility\nchecks to be performed. The following constants define the possible values of\nmode. It is possible to create a mask consisting of the bitwise OR of two or\nmore values (e.g. fs.constants.W_OK | fs.constants.R_OK).
fs.constants.F_OK - path is visible to the calling process. This is useful\nfor determining if a file exists, but says nothing about rwx permissions.\nDefault if no mode is specified.fs.constants.R_OK - path can be read by the calling process.fs.constants.W_OK - path can be written by the calling process.fs.constants.X_OK - path can be executed by the calling process. This has\nno effect on Windows (will behave like fs.constants.F_OK).The final argument, callback, is a callback function that is invoked with\na possible error argument. If any of the accessibility checks fail, the error\nargument will be an Error object. The following example checks if the file\n/etc/passwd can be read and written by the current process.
fs.access('/etc/passwd', fs.constants.R_OK | fs.constants.W_OK, (err) => {\n console.log(err ? 'no access!' : 'can read/write');\n});\nUsing fs.access() to check for the accessibility of a file before calling\nfs.open(), fs.readFile() or fs.writeFile() is not recommended. Doing\nso introduces a race condition, since other processes may change the file's\nstate between the two calls. Instead, user code should open/read/write the\nfile directly and handle the error raised if the file is not accessible.
write (NOT RECOMMENDED)
\nfs.access('myfile', (err) => {\n if (!err) {\n console.error('myfile already exists');\n return;\n }\n\n fs.open('myfile', 'wx', (err, fd) => {\n if (err) throw err;\n writeMyData(fd);\n });\n});\nwrite (RECOMMENDED)
\nfs.open('myfile', 'wx', (err, fd) => {\n if (err) {\n if (err.code === 'EEXIST') {\n console.error('myfile already exists');\n return;\n }\n\n throw err;\n }\n\n writeMyData(fd);\n});\nread (NOT RECOMMENDED)
\nfs.access('myfile', (err) => {\n if (err) {\n if (err.code === 'ENOENT') {\n console.error('myfile does not exist');\n return;\n }\n\n throw err;\n }\n\n fs.open('myfile', 'r', (err, fd) => {\n if (err) throw err;\n readMyData(fd);\n });\n});\nread (RECOMMENDED)
\nfs.open('myfile', 'r', (err, fd) => {\n if (err) {\n if (err.code === 'ENOENT') {\n console.error('myfile does not exist');\n return;\n }\n\n throw err;\n }\n\n readMyData(fd);\n});\nThe "not recommended" examples above check for accessibility and then use the\nfile; the "recommended" examples are better because they use the file directly\nand handle the error, if any.
\nIn general, check for the accessibility of a file only if the file will not be\nused directly, for example when its accessibility is a signal from another\nprocess.
\n" }, { "textRaw": "fs.accessSync(path[, mode])", "type": "method", "name": "accessSync", "meta": { "added": [ "v0.11.15" ], "changes": [ { "version": "v7.6.0", "pr-url": "https://github.com/nodejs/node/pull/10739", "description": "The `path` parameter can be a WHATWG `URL` object using `file:` protocol. Support is currently still *experimental*." } ] }, "signatures": [ { "params": [ { "textRaw": "`path` {string|Buffer|URL} ", "name": "path", "type": "string|Buffer|URL" }, { "textRaw": "`mode` {integer} **Default:** `fs.constants.F_OK` ", "name": "mode", "type": "integer", "default": "`fs.constants.F_OK`", "optional": true } ] }, { "params": [ { "name": "path" }, { "name": "mode", "optional": true } ] } ], "desc": "Synchronously tests a user's permissions for the file or directory specified by\npath. The mode argument is an optional integer that specifies the\naccessibility checks to be performed. The following constants define the\npossible values of mode. It is possible to create a mask consisting of the\nbitwise OR of two or more values (e.g. fs.constants.W_OK | fs.constants.R_OK).
fs.constants.F_OK - path is visible to the calling process. This is useful\nfor determining if a file exists, but says nothing about rwx permissions.\nDefault if no mode is specified.fs.constants.R_OK - path can be read by the calling process.fs.constants.W_OK - path can be written by the calling process.fs.constants.X_OK - path can be executed by the calling process. This has\nno effect on Windows (will behave like fs.constants.F_OK).If any of the accessibility checks fail, an Error will be thrown. Otherwise,\nthe method will return undefined.
try {\n fs.accessSync('etc/passwd', fs.constants.R_OK | fs.constants.W_OK);\n console.log('can read/write');\n} catch (err) {\n console.error('no access!');\n}\nAsynchronously append data to a file, creating the file if it does not yet\nexist. data can be a string or a Buffer.
Example:
\nfs.appendFile('message.txt', 'data to append', (err) => {\n if (err) throw err;\n console.log('The "data to append" was appended to file!');\n});\nIf options is a string, then it specifies the encoding. Example:
fs.appendFile('message.txt', 'data to append', 'utf8', callback);\nThe file may be specified as a numeric file descriptor that has been opened\nfor appending (using fs.open() or fs.openSync()). The file descriptor will\nnot be closed automatically.
fs.open('message.txt', 'a', (err, fd) => {\n if (err) throw err;\n fs.appendFile(fd, 'data to append', 'utf8', (err) => {\n fs.close(fd, (err) => {\n if (err) throw err;\n });\n if (err) throw err;\n });\n});\nSynchronously append data to a file, creating the file if it does not yet\nexist. data can be a string or a Buffer.
Example:
\ntry {\n fs.appendFileSync('message.txt', 'data to append');\n console.log('The "data to append" was appended to file!');\n} catch (err) {\n /* Handle the error */\n}\nIf options is a string, then it specifies the encoding. Example:
fs.appendFileSync('message.txt', 'data to append', 'utf8');\nThe file may be specified as a numeric file descriptor that has been opened\nfor appending (using fs.open() or fs.openSync()). The file descriptor will\nnot be closed automatically.
let fd;\n\ntry {\n fd = fs.openSync('message.txt', 'a');\n fs.appendFileSync(fd, 'data to append', 'utf8');\n} catch (err) {\n /* Handle the error */\n} finally {\n if (fd !== undefined)\n fs.closeSync(fd);\n}\nAsynchronously changes the permissions of a file. No arguments other than a\npossible exception are given to the completion callback.
\nSee also: chmod(2)
\n", "modules": [ { "textRaw": "File modes", "name": "file_modes", "desc": "The mode argument used in both the fs.chmod() and fs.chmodSync()\nmethods is a numeric bitmask created using a logical OR of the following\nconstants:
| Constant | \nOctal | \nDescription | \n
|---|---|---|
fs.constants.S_IRUSR | \n0o400 | \nread by owner | \n
fs.constants.S_IWUSR | \n0o200 | \nwrite by owner | \n
fs.constants.S_IXUSR | \n0o100 | \nexecute/search by owner | \n
fs.constants.S_IRGRP | \n0o40 | \nread by group | \n
fs.constants.S_IWGRP | \n0o20 | \nwrite by group | \n
fs.constants.S_IXGRP | \n0o10 | \nexecute/search by group | \n
fs.constants.S_IROTH | \n0o4 | \nread by others | \n
fs.constants.S_IWOTH | \n0o2 | \nwrite by others | \n
fs.constants.S_IXOTH | \n0o1 | \nexecute/search by others | \n
An easier method of constructing the mode is to use a sequence of three\noctal digits (e.g. 765). The left-most digit (7 in the example), specifies\nthe permissions for the file owner. The middle digit (6 in the example),\nspecifies permissions for the group. The right-most digit (5 in the example),\nspecifies the permissions for others.
| Number | \nDescription | \n
|---|---|
7 | \nread, write, and execute | \n
6 | \nread and write | \n
5 | \nread and execute | \n
4 | \nread only | \n
3 | \nwrite and execute | \n
2 | \nwrite only | \n
1 | \nexecute only | \n
0 | \nno permission | \n
For example, the octal value 0o765 means:
Synchronously changes the permissions of a file. Returns undefined.\nThis is the synchronous version of fs.chmod().
See also: chmod(2)
\n" }, { "textRaw": "fs.chown(path, uid, gid, callback)", "type": "method", "name": "chown", "meta": { "added": [ "v0.1.97" ], "changes": [ { "version": "REPLACEME", "pr-url": "https://github.com/nodejs/node/pull/12562", "description": "The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime." }, { "version": "v7.6.0", "pr-url": "https://github.com/nodejs/node/pull/10739", "description": "The `path` parameter can be a WHATWG `URL` object using `file:` protocol. Support is currently still *experimental*." }, { "version": "v7.0.0", "pr-url": "https://github.com/nodejs/node/pull/7897", "description": "The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013." } ] }, "signatures": [ { "params": [ { "textRaw": "`path` {string|Buffer|URL} ", "name": "path", "type": "string|Buffer|URL" }, { "textRaw": "`uid` {integer} ", "name": "uid", "type": "integer" }, { "textRaw": "`gid` {integer} ", "name": "gid", "type": "integer" }, { "textRaw": "`callback` {Function} ", "options": [ { "textRaw": "`err` {Error} ", "name": "err", "type": "Error" } ], "name": "callback", "type": "Function" } ] }, { "params": [ { "name": "path" }, { "name": "uid" }, { "name": "gid" }, { "name": "callback" } ] } ], "desc": "Asynchronously changes owner and group of a file. No arguments other than a\npossible exception are given to the completion callback.
\nSee also: chown(2)
\n" }, { "textRaw": "fs.chownSync(path, uid, gid)", "type": "method", "name": "chownSync", "meta": { "added": [ "v0.1.97" ], "changes": [ { "version": "v7.6.0", "pr-url": "https://github.com/nodejs/node/pull/10739", "description": "The `path` parameter can be a WHATWG `URL` object using `file:` protocol. Support is currently still *experimental*." } ] }, "signatures": [ { "params": [ { "textRaw": "`path` {string|Buffer|URL} ", "name": "path", "type": "string|Buffer|URL" }, { "textRaw": "`uid` {integer} ", "name": "uid", "type": "integer" }, { "textRaw": "`gid` {integer} ", "name": "gid", "type": "integer" } ] }, { "params": [ { "name": "path" }, { "name": "uid" }, { "name": "gid" } ] } ], "desc": "Synchronously changes owner and group of a file. Returns undefined.\nThis is the synchronous version of fs.chown().
See also: chown(2)
\n" }, { "textRaw": "fs.close(fd, callback)", "type": "method", "name": "close", "meta": { "added": [ "v0.0.2" ], "changes": [ { "version": "REPLACEME", "pr-url": "https://github.com/nodejs/node/pull/12562", "description": "The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime." }, { "version": "v7.0.0", "pr-url": "https://github.com/nodejs/node/pull/7897", "description": "The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013." } ] }, "signatures": [ { "params": [ { "textRaw": "`fd` {integer} ", "name": "fd", "type": "integer" }, { "textRaw": "`callback` {Function} ", "options": [ { "textRaw": "`err` {Error} ", "name": "err", "type": "Error" } ], "name": "callback", "type": "Function" } ] }, { "params": [ { "name": "fd" }, { "name": "callback" } ] } ], "desc": "Asynchronous close(2). No arguments other than a possible exception are given\nto the completion callback.
\n" }, { "textRaw": "fs.closeSync(fd)", "type": "method", "name": "closeSync", "meta": { "added": [ "v0.1.21" ], "changes": [] }, "signatures": [ { "params": [ { "textRaw": "`fd` {integer} ", "name": "fd", "type": "integer" } ] }, { "params": [ { "name": "fd" } ] } ], "desc": "Synchronous close(2). Returns undefined.
Asynchronously copies src to dest. By default, dest is overwritten if it\nalready exists. No arguments other than a possible exception are given to the\ncallback function. Node.js makes no guarantees about the atomicity of the copy\noperation. If an error occurs after the destination file has been opened for\nwriting, Node.js will attempt to remove the destination.
flags is an optional integer that specifies the behavior\nof the copy operation. It is possible to create a mask consisting of the bitwise\nOR of two or more values (e.g.\nfs.constants.COPYFILE_EXCL | fs.constants.COPYFILE_FICLONE).
fs.constants.COPYFILE_EXCL - The copy operation will fail if dest already\nexists.fs.constants.COPYFILE_FICLONE - The copy operation will attempt to create a\ncopy-on-write reflink. If the platform does not support copy-on-write, then a\nfallback copy mechanism is used.fs.constants.COPYFILE_FICLONE_FORCE - The copy operation will attempt to\ncreate a copy-on-write reflink. If the platform does not support copy-on-write,\nthen the operation will fail.Example:
\nconst fs = require('fs');\n\n// destination.txt will be created or overwritten by default.\nfs.copyFile('source.txt', 'destination.txt', (err) => {\n if (err) throw err;\n console.log('source.txt was copied to destination.txt');\n});\nIf the third argument is a number, then it specifies flags, as shown in the\nfollowing example.
const fs = require('fs');\nconst { COPYFILE_EXCL } = fs.constants;\n\n// By using COPYFILE_EXCL, the operation will fail if destination.txt exists.\nfs.copyFile('source.txt', 'destination.txt', COPYFILE_EXCL, callback);\nSynchronously copies src to dest. By default, dest is overwritten if it\nalready exists. Returns undefined. Node.js makes no guarantees about the\natomicity of the copy operation. If an error occurs after the destination file\nhas been opened for writing, Node.js will attempt to remove the destination.
flags is an optional integer that specifies the behavior\nof the copy operation. It is possible to create a mask consisting of the bitwise\nOR of two or more values (e.g.\nfs.constants.COPYFILE_EXCL | fs.constants.COPYFILE_FICLONE).
fs.constants.COPYFILE_EXCL - The copy operation will fail if dest already\nexists.fs.constants.COPYFILE_FICLONE - The copy operation will attempt to create a\ncopy-on-write reflink. If the platform does not support copy-on-write, then a\nfallback copy mechanism is used.fs.constants.COPYFILE_FICLONE_FORCE - The copy operation will attempt to\ncreate a copy-on-write reflink. If the platform does not support copy-on-write,\nthen the operation will fail.Example:
\nconst fs = require('fs');\n\n// destination.txt will be created or overwritten by default.\nfs.copyFileSync('source.txt', 'destination.txt');\nconsole.log('source.txt was copied to destination.txt');\nIf the third argument is a number, then it specifies flags, as shown in the\nfollowing example.
const fs = require('fs');\nconst { COPYFILE_EXCL } = fs.constants;\n\n// By using COPYFILE_EXCL, the operation will fail if destination.txt exists.\nfs.copyFileSync('source.txt', 'destination.txt', COPYFILE_EXCL);\nBe aware that, unlike the default value set for highWaterMark on a\nreadable stream (16 kb), the stream returned by this method has a\ndefault value of 64 kb for the same parameter.
options can include start and end values to read a range of bytes from\nthe file instead of the entire file. Both start and end are inclusive and\nstart counting at 0. If fd is specified and start is omitted or undefined,\nfs.createReadStream() reads sequentially from the current file position.\nThe encoding can be any one of those accepted by Buffer.
If fd is specified, ReadStream will ignore the path argument and will use\nthe specified file descriptor. This means that no 'open' event will be\nemitted. Note that fd should be blocking; non-blocking fds should be passed\nto net.Socket.
If autoClose is false, then the file descriptor won't be closed, even if\nthere's an error. It is the application's responsibility to close it and make\nsure there's no file descriptor leak. If autoClose is set to true (default\nbehavior), on 'error' or 'end' the file descriptor will be closed\nautomatically.
mode sets the file mode (permission and sticky bits), but only if the\nfile was created.
An example to read the last 10 bytes of a file which is 100 bytes long:
\nfs.createReadStream('sample.txt', { start: 90, end: 99 });\nIf options is a string, then it specifies the encoding.
options may also include a start option to allow writing data at\nsome position past the beginning of the file. Modifying a file rather\nthan replacing it may require a flags mode of r+ rather than the\ndefault mode w. The encoding can be any one of those accepted by\nBuffer.
If autoClose is set to true (default behavior) on 'error' or 'finish'\nthe file descriptor will be closed automatically. If autoClose is false,\nthen the file descriptor won't be closed, even if there's an error.\nIt is the application's responsibility to close it and make sure there's no\nfile descriptor leak.
Like ReadStream, if fd is specified, WriteStream will ignore the\npath argument and will use the specified file descriptor. This means that no\n'open' event will be emitted. Note that fd should be blocking; non-blocking\nfds should be passed to net.Socket.
If options is a string, then it specifies the encoding.
Test whether or not the given path exists by checking with the file system.\nThen call the callback argument with either true or false. Example:
fs.exists('/etc/passwd', (exists) => {\n console.log(exists ? 'it\\'s there' : 'no passwd!');\n});\nNote that the parameter to this callback is not consistent with other\nNode.js callbacks. Normally, the first parameter to a Node.js callback is\nan err parameter, optionally followed by other parameters. The\nfs.exists() callback has only one boolean parameter. This is one reason\nfs.access() is recommended instead of fs.exists().
Using fs.exists() to check for the existence of a file before calling\nfs.open(), fs.readFile() or fs.writeFile() is not recommended. Doing\nso introduces a race condition, since other processes may change the file's\nstate between the two calls. Instead, user code should open/read/write the\nfile directly and handle the error raised if the file does not exist.
write (NOT RECOMMENDED)
\nfs.exists('myfile', (exists) => {\n if (exists) {\n console.error('myfile already exists');\n } else {\n fs.open('myfile', 'wx', (err, fd) => {\n if (err) throw err;\n writeMyData(fd);\n });\n }\n});\nwrite (RECOMMENDED)
\nfs.open('myfile', 'wx', (err, fd) => {\n if (err) {\n if (err.code === 'EEXIST') {\n console.error('myfile already exists');\n return;\n }\n\n throw err;\n }\n\n writeMyData(fd);\n});\nread (NOT RECOMMENDED)
\nfs.exists('myfile', (exists) => {\n if (exists) {\n fs.open('myfile', 'r', (err, fd) => {\n if (err) throw err;\n readMyData(fd);\n });\n } else {\n console.error('myfile does not exist');\n }\n});\nread (RECOMMENDED)
\nfs.open('myfile', 'r', (err, fd) => {\n if (err) {\n if (err.code === 'ENOENT') {\n console.error('myfile does not exist');\n return;\n }\n\n throw err;\n }\n\n readMyData(fd);\n});\nThe "not recommended" examples above check for existence and then use the\nfile; the "recommended" examples are better because they use the file directly\nand handle the error, if any.
\nIn general, check for the existence of a file only if the file won’t be\nused directly, for example when its existence is a signal from another\nprocess.
\n" }, { "textRaw": "fs.existsSync(path)", "type": "method", "name": "existsSync", "meta": { "added": [ "v0.1.21" ], "changes": [ { "version": "v7.6.0", "pr-url": "https://github.com/nodejs/node/pull/10739", "description": "The `path` parameter can be a WHATWG `URL` object using `file:` protocol. Support is currently still *experimental*." } ] }, "signatures": [ { "return": { "textRaw": "Returns: {boolean} ", "name": "return", "type": "boolean" }, "params": [ { "textRaw": "`path` {string|Buffer|URL} ", "name": "path", "type": "string|Buffer|URL" } ] }, { "params": [ { "name": "path" } ] } ], "desc": "Synchronous version of fs.exists().\nReturns true if the path exists, false otherwise.
Note that fs.exists() is deprecated, but fs.existsSync() is not.\n(The callback parameter to fs.exists() accepts parameters that are\ninconsistent with other Node.js callbacks. fs.existsSync() does not use\na callback.)
Asynchronous fchmod(2). No arguments other than a possible exception\nare given to the completion callback.
\n" }, { "textRaw": "fs.fchmodSync(fd, mode)", "type": "method", "name": "fchmodSync", "meta": { "added": [ "v0.4.7" ], "changes": [] }, "signatures": [ { "params": [ { "textRaw": "`fd` {integer} ", "name": "fd", "type": "integer" }, { "textRaw": "`mode` {integer} ", "name": "mode", "type": "integer" } ] }, { "params": [ { "name": "fd" }, { "name": "mode" } ] } ], "desc": "Synchronous fchmod(2). Returns undefined.
Asynchronous fchown(2). No arguments other than a possible exception are given\nto the completion callback.
\n" }, { "textRaw": "fs.fchownSync(fd, uid, gid)", "type": "method", "name": "fchownSync", "meta": { "added": [ "v0.4.7" ], "changes": [] }, "signatures": [ { "params": [ { "textRaw": "`fd` {integer} ", "name": "fd", "type": "integer" }, { "textRaw": "`uid` {integer} ", "name": "uid", "type": "integer" }, { "textRaw": "`gid` {integer} ", "name": "gid", "type": "integer" } ] }, { "params": [ { "name": "fd" }, { "name": "uid" }, { "name": "gid" } ] } ], "desc": "Synchronous fchown(2). Returns undefined.
Asynchronous fdatasync(2). No arguments other than a possible exception are\ngiven to the completion callback.
\n" }, { "textRaw": "fs.fdatasyncSync(fd)", "type": "method", "name": "fdatasyncSync", "meta": { "added": [ "v0.1.96" ], "changes": [] }, "signatures": [ { "params": [ { "textRaw": "`fd` {integer} ", "name": "fd", "type": "integer" } ] }, { "params": [ { "name": "fd" } ] } ], "desc": "Synchronous fdatasync(2). Returns undefined.
Asynchronous fstat(2). The callback gets two arguments (err, stats) where\nstats is an fs.Stats object. fstat() is identical to stat(),\nexcept that the file to be stat-ed is specified by the file descriptor fd.
Synchronous fstat(2).
\n" }, { "textRaw": "fs.fsync(fd, callback)", "type": "method", "name": "fsync", "meta": { "added": [ "v0.1.96" ], "changes": [ { "version": "REPLACEME", "pr-url": "https://github.com/nodejs/node/pull/12562", "description": "The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime." }, { "version": "v7.0.0", "pr-url": "https://github.com/nodejs/node/pull/7897", "description": "The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013." } ] }, "signatures": [ { "params": [ { "textRaw": "`fd` {integer} ", "name": "fd", "type": "integer" }, { "textRaw": "`callback` {Function} ", "options": [ { "textRaw": "`err` {Error} ", "name": "err", "type": "Error" } ], "name": "callback", "type": "Function" } ] }, { "params": [ { "name": "fd" }, { "name": "callback" } ] } ], "desc": "Asynchronous fsync(2). No arguments other than a possible exception are given\nto the completion callback.
\n" }, { "textRaw": "fs.fsyncSync(fd)", "type": "method", "name": "fsyncSync", "meta": { "added": [ "v0.1.96" ], "changes": [] }, "signatures": [ { "params": [ { "textRaw": "`fd` {integer} ", "name": "fd", "type": "integer" } ] }, { "params": [ { "name": "fd" } ] } ], "desc": "Synchronous fsync(2). Returns undefined.
Asynchronous ftruncate(2). No arguments other than a possible exception are\ngiven to the completion callback.
\nIf the file referred to by the file descriptor was larger than len bytes, only\nthe first len bytes will be retained in the file.
For example, the following program retains only the first four bytes of the file
\nconsole.log(fs.readFileSync('temp.txt', 'utf8'));\n// Prints: Node.js\n\n// get the file descriptor of the file to be truncated\nconst fd = fs.openSync('temp.txt', 'r+');\n\n// truncate the file to first four bytes\nfs.ftruncate(fd, 4, (err) => {\n assert.ifError(err);\n console.log(fs.readFileSync('temp.txt', 'utf8'));\n});\n// Prints: Node\nIf the file previously was shorter than len bytes, it is extended, and the\nextended part is filled with null bytes ('\\0'). For example,
console.log(fs.readFileSync('temp.txt', 'utf8'));\n// Prints: Node.js\n\n// get the file descriptor of the file to be truncated\nconst fd = fs.openSync('temp.txt', 'r+');\n\n// truncate the file to 10 bytes, whereas the actual size is 7 bytes\nfs.ftruncate(fd, 10, (err) => {\n assert.ifError(err);\n console.log(fs.readFileSync('temp.txt'));\n});\n// Prints: <Buffer 4e 6f 64 65 2e 6a 73 00 00 00>\n// ('Node.js\\0\\0\\0' in UTF8)\nThe last three bytes are null bytes ('\\0'), to compensate the over-truncation.
\n" }, { "textRaw": "fs.ftruncateSync(fd[, len])", "type": "method", "name": "ftruncateSync", "meta": { "added": [ "v0.8.6" ], "changes": [] }, "signatures": [ { "params": [ { "textRaw": "`fd` {integer} ", "name": "fd", "type": "integer" }, { "textRaw": "`len` {integer} **Default:** `0` ", "name": "len", "type": "integer", "default": "`0`", "optional": true } ] }, { "params": [ { "name": "fd" }, { "name": "len", "optional": true } ] } ], "desc": "Synchronous ftruncate(2). Returns undefined.
Change the file system timestamps of the object referenced by the supplied file\ndescriptor. See fs.utimes().
This function does not work on AIX versions before 7.1, it will return the\nerror UV_ENOSYS.
Synchronous version of fs.futimes(). Returns undefined.
Asynchronous lchmod(2). No arguments other than a possible exception\nare given to the completion callback.
\nOnly available on macOS.
\n" }, { "textRaw": "fs.lchmodSync(path, mode)", "type": "method", "name": "lchmodSync", "meta": { "deprecated": [ "v0.4.7" ], "changes": [] }, "signatures": [ { "params": [ { "textRaw": "`path` {string|Buffer|URL} ", "name": "path", "type": "string|Buffer|URL" }, { "textRaw": "`mode` {integer} ", "name": "mode", "type": "integer" } ] }, { "params": [ { "name": "path" }, { "name": "mode" } ] } ], "desc": "Synchronous lchmod(2). Returns undefined.
Asynchronous lchown(2). No arguments other than a possible exception are given\nto the completion callback.
\n" }, { "textRaw": "fs.lchownSync(path, uid, gid)", "type": "method", "name": "lchownSync", "meta": { "deprecated": [ "v0.4.7" ], "changes": [] }, "signatures": [ { "params": [ { "textRaw": "`path` {string|Buffer|URL} ", "name": "path", "type": "string|Buffer|URL" }, { "textRaw": "`uid` {integer} ", "name": "uid", "type": "integer" }, { "textRaw": "`gid` {integer} ", "name": "gid", "type": "integer" } ] }, { "params": [ { "name": "path" }, { "name": "uid" }, { "name": "gid" } ] } ], "desc": "Synchronous lchown(2). Returns undefined.
Asynchronous link(2). No arguments other than a possible exception are given to\nthe completion callback.
\n" }, { "textRaw": "fs.linkSync(existingPath, newPath)", "type": "method", "name": "linkSync", "meta": { "added": [ "v0.1.31" ], "changes": [ { "version": "v7.6.0", "pr-url": "https://github.com/nodejs/node/pull/10739", "description": "The `existingPath` and `newPath` parameters can be WHATWG `URL` objects using `file:` protocol. Support is currently still *experimental*." } ] }, "signatures": [ { "params": [ { "textRaw": "`existingPath` {string|Buffer|URL} ", "name": "existingPath", "type": "string|Buffer|URL" }, { "textRaw": "`newPath` {string|Buffer|URL} ", "name": "newPath", "type": "string|Buffer|URL" } ] }, { "params": [ { "name": "existingPath" }, { "name": "newPath" } ] } ], "desc": "Synchronous link(2). Returns undefined.
Asynchronous lstat(2). The callback gets two arguments (err, stats) where\nstats is a fs.Stats object. lstat() is identical to stat(),\nexcept that if path is a symbolic link, then the link itself is stat-ed,\nnot the file that it refers to.
Synchronous lstat(2).
\n" }, { "textRaw": "fs.mkdir(path[, mode], callback)", "type": "method", "name": "mkdir", "meta": { "added": [ "v0.1.8" ], "changes": [ { "version": "REPLACEME", "pr-url": "https://github.com/nodejs/node/pull/12562", "description": "The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime." }, { "version": "v7.6.0", "pr-url": "https://github.com/nodejs/node/pull/10739", "description": "The `path` parameter can be a WHATWG `URL` object using `file:` protocol. Support is currently still *experimental*." }, { "version": "v7.0.0", "pr-url": "https://github.com/nodejs/node/pull/7897", "description": "The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013." } ] }, "signatures": [ { "params": [ { "textRaw": "`path` {string|Buffer|URL} ", "name": "path", "type": "string|Buffer|URL" }, { "textRaw": "`mode` {integer} **Default:** `0o777` ", "name": "mode", "type": "integer", "default": "`0o777`", "optional": true }, { "textRaw": "`callback` {Function} ", "options": [ { "textRaw": "`err` {Error} ", "name": "err", "type": "Error" } ], "name": "callback", "type": "Function" } ] }, { "params": [ { "name": "path" }, { "name": "mode", "optional": true }, { "name": "callback" } ] } ], "desc": "Asynchronously creates a directory. No arguments other than a possible exception\nare given to the completion callback.
\nSee also: mkdir(2)
\n" }, { "textRaw": "fs.mkdirSync(path[, mode])", "type": "method", "name": "mkdirSync", "meta": { "added": [ "v0.1.21" ], "changes": [ { "version": "v7.6.0", "pr-url": "https://github.com/nodejs/node/pull/10739", "description": "The `path` parameter can be a WHATWG `URL` object using `file:` protocol. Support is currently still *experimental*." } ] }, "signatures": [ { "params": [ { "textRaw": "`path` {string|Buffer|URL} ", "name": "path", "type": "string|Buffer|URL" }, { "textRaw": "`mode` {integer} **Default:** `0o777` ", "name": "mode", "type": "integer", "default": "`0o777`", "optional": true } ] }, { "params": [ { "name": "path" }, { "name": "mode", "optional": true } ] } ], "desc": "Synchronously creates a directory. Returns undefined.\nThis is the synchronous version of fs.mkdir().
See also: mkdir(2)
\n" }, { "textRaw": "fs.mkdtemp(prefix[, options], callback)", "type": "method", "name": "mkdtemp", "meta": { "added": [ "v5.10.0" ], "changes": [ { "version": "REPLACEME", "pr-url": "https://github.com/nodejs/node/pull/12562", "description": "The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime." }, { "version": "v7.0.0", "pr-url": "https://github.com/nodejs/node/pull/7897", "description": "The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013." }, { "version": "v6.2.1", "pr-url": "https://github.com/nodejs/node/pull/6828", "description": "The `callback` parameter is optional now." } ] }, "signatures": [ { "params": [ { "textRaw": "`prefix` {string} ", "name": "prefix", "type": "string" }, { "textRaw": "`options` {string|Object} ", "options": [ { "textRaw": "`encoding` {string} **Default:** `'utf8'` ", "name": "encoding", "type": "string", "default": "`'utf8'`" } ], "name": "options", "type": "string|Object", "optional": true }, { "textRaw": "`callback` {Function} ", "options": [ { "textRaw": "`err` {Error} ", "name": "err", "type": "Error" }, { "textRaw": "`folder` {string} ", "name": "folder", "type": "string" } ], "name": "callback", "type": "Function" } ] }, { "params": [ { "name": "prefix" }, { "name": "options", "optional": true }, { "name": "callback" } ] } ], "desc": "Creates a unique temporary directory.
\nGenerates six random characters to be appended behind a required\nprefix to create a unique temporary directory.
The created folder path is passed as a string to the callback's second\nparameter.
\nThe optional options argument can be a string specifying an encoding, or an\nobject with an encoding property specifying the character encoding to use.
Example:
\nfs.mkdtemp(path.join(os.tmpdir(), 'foo-'), (err, folder) => {\n if (err) throw err;\n console.log(folder);\n // Prints: /tmp/foo-itXde2 or C:\\Users\\...\\AppData\\Local\\Temp\\foo-itXde2\n});\nThe fs.mkdtemp() method will append the six randomly selected characters\ndirectly to the prefix string. For instance, given a directory /tmp, if the\nintention is to create a temporary directory within /tmp, the prefix\nmust end with a trailing platform-specific path separator\n(require('path').sep).
// The parent directory for the new temporary directory\nconst tmpDir = os.tmpdir();\n\n// This method is *INCORRECT*:\nfs.mkdtemp(tmpDir, (err, folder) => {\n if (err) throw err;\n console.log(folder);\n // Will print something similar to `/tmpabc123`.\n // Note that a new temporary directory is created\n // at the file system root rather than *within*\n // the /tmp directory.\n});\n\n// This method is *CORRECT*:\nconst { sep } = require('path');\nfs.mkdtemp(`${tmpDir}${sep}`, (err, folder) => {\n if (err) throw err;\n console.log(folder);\n // Will print something similar to `/tmp/abc123`.\n // A new temporary directory is created within\n // the /tmp directory.\n});\nThe synchronous version of fs.mkdtemp(). Returns the created\nfolder path.
The optional options argument can be a string specifying an encoding, or an\nobject with an encoding property specifying the character encoding to use.
Asynchronous file open. See open(2). flags can be:
'r' - Open file for reading.\nAn exception occurs if the file does not exist.
'r+' - Open file for reading and writing.\nAn exception occurs if the file does not exist.
'rs+' - Open file for reading and writing in synchronous mode. Instructs\nthe operating system to bypass the local file system cache.
This is primarily useful for opening files on NFS mounts as it allows skipping\nthe potentially stale local cache. It has a very real impact on I/O\nperformance so using this flag is not recommended unless it is needed.
\nNote that this doesn't turn fs.open() into a synchronous blocking call.\nIf synchronous operation is desired fs.openSync() should be used.
'w' - Open file for writing.\nThe file is created (if it does not exist) or truncated (if it exists).
'wx' - Like 'w' but fails if path exists.
'w+' - Open file for reading and writing.\nThe file is created (if it does not exist) or truncated (if it exists).
'wx+' - Like 'w+' but fails if path exists.
'a' - Open file for appending.\nThe file is created if it does not exist.
'ax' - Like 'a' but fails if path exists.
'as' - Open file for appending in synchronous mode.\nThe file is created if it does not exist.
'a+' - Open file for reading and appending.\nThe file is created if it does not exist.
'ax+' - Like 'a+' but fails if path exists.
'as+' - Open file for reading and appending in synchronous mode.\nThe file is created if it does not exist.
mode sets the file mode (permission and sticky bits), but only if the file was\ncreated.
The callback gets two arguments (err, fd).
The exclusive flag 'x' (O_EXCL flag in open(2)) ensures that path is newly\ncreated. On POSIX systems, path is considered to exist even if it is a symlink\nto a non-existent file. The exclusive flag may or may not work with network file\nsystems.
flags can also be a number as documented by open(2); commonly used constants\nare available from fs.constants. On Windows, flags are translated to\ntheir equivalent ones where applicable, e.g. O_WRONLY to FILE_GENERIC_WRITE,\nor O_EXCL|O_CREAT to CREATE_NEW, as accepted by CreateFileW.
On Linux, positional writes don't work when the file is opened in append mode.\nThe kernel ignores the position argument and always appends the data to\nthe end of the file.
\nThe behavior of fs.open() is platform-specific for some flags. As such,\nopening a directory on macOS and Linux with the 'a+' flag - see example\nbelow - will return an error. In contrast, on Windows and FreeBSD, a file\ndescriptor will be returned.
// macOS and Linux\nfs.open('<directory>', 'a+', (err, fd) => {\n // => [Error: EISDIR: illegal operation on a directory, open <directory>]\n});\n\n// Windows and FreeBSD\nfs.open('<directory>', 'a+', (err, fd) => {\n // => null, <fd>\n});\nSome characters (< > : " / \\ | ? *) are reserved under Windows as documented\nby Naming Files, Paths, and Namespaces. Under NTFS, if the filename contains\na colon, Node.js will open a file system stream, as described by\nthis MSDN page.
Functions based on fs.open() exhibit this behavior as well. eg.\nfs.writeFile(), fs.readFile(), etc.
Note: On Windows, opening an existing hidden file using the w flag (either\nthrough fs.open() or fs.writeFile()) will fail with EPERM. Existing hidden\nfiles can be opened for writing with the r+ flag. A call to fs.ftruncate()\ncan be used to reset the file contents.
Synchronous version of fs.open(). Returns an integer representing the file\ndescriptor.
Read data from the file specified by fd.
buffer is the buffer that the data will be written to.
offset is the offset in the buffer to start writing at.
length is an integer specifying the number of bytes to read.
position is an argument specifying where to begin reading from in the file.\nIf position is null, data will be read from the current file position,\nand the file position will be updated.\nIf position is an integer, the file position will remain unchanged.
The callback is given the three arguments, (err, bytesRead, buffer).
If this method is invoked as its util.promisify()ed version, it returns\na Promise for an object with bytesRead and buffer properties.
Asynchronous readdir(3). Reads the contents of a directory.\nThe callback gets two arguments (err, files) where files is an array of\nthe names of the files in the directory excluding '.' and '..'.
The optional options argument can be a string specifying an encoding, or an\nobject with an encoding property specifying the character encoding to use for\nthe filenames passed to the callback. If the encoding is set to 'buffer',\nthe filenames returned will be passed as Buffer objects.
Synchronous readdir(3).
\nThe optional options argument can be a string specifying an encoding, or an\nobject with an encoding property specifying the character encoding to use for\nthe filenames passed to the callback. If the encoding is set to 'buffer',\nthe filenames returned will be passed as Buffer objects.
Asynchronously reads the entire contents of a file. Example:
\nfs.readFile('/etc/passwd', (err, data) => {\n if (err) throw err;\n console.log(data);\n});\nThe callback is passed two arguments (err, data), where data is the\ncontents of the file.
If no encoding is specified, then the raw buffer is returned.
\nIf options is a string, then it specifies the encoding. Example:
fs.readFile('/etc/passwd', 'utf8', callback);\nWhen the path is a directory, the behavior of fs.readFile() and\nfs.readFileSync() is platform-specific. On macOS, Linux, and Windows, an\nerror will be returned. On FreeBSD, a representation of the directory's contents\nwill be returned.
// macOS, Linux, and Windows\nfs.readFile('<directory>', (err, data) => {\n // => [Error: EISDIR: illegal operation on a directory, read <directory>]\n});\n\n// FreeBSD\nfs.readFile('<directory>', (err, data) => {\n // => null, <data>\n});\nAny specified file descriptor has to support reading.
\nIf a file descriptor is specified as the path, it will not be closed\nautomatically.
The fs.readFile() function buffers the entire file. To minimize memory costs,\nwhen possible prefer streaming via fs.createReadStream().
Synchronous version of fs.readFile(). Returns the contents of the path.
If the encoding option is specified then this function returns a\nstring. Otherwise it returns a buffer.
Similar to fs.readFile(), when the path is a directory, the behavior of\nfs.readFileSync() is platform-specific.
// macOS, Linux, and Windows\nfs.readFileSync('<directory>');\n// => [Error: EISDIR: illegal operation on a directory, read <directory>]\n\n// FreeBSD\nfs.readFileSync('<directory>'); // => null, <data>\nAsynchronous readlink(2). The callback gets two arguments (err,\nlinkString).
The optional options argument can be a string specifying an encoding, or an\nobject with an encoding property specifying the character encoding to use for\nthe link path passed to the callback. If the encoding is set to 'buffer',\nthe link path returned will be passed as a Buffer object.
Synchronous readlink(2). Returns the symbolic link's string value.
\nThe optional options argument can be a string specifying an encoding, or an\nobject with an encoding property specifying the character encoding to use for\nthe link path passed to the callback. If the encoding is set to 'buffer',\nthe link path returned will be passed as a Buffer object.
Synchronous version of fs.read(). Returns the number of bytesRead.
Asynchronously computes the canonical pathname by resolving ., .. and\nsymbolic links.
Note that "canonical" does not mean "unique": hard links and bind mounts can\nexpose a file system entity through many pathnames.
\nThis function behaves like realpath(3), with some exceptions:
\nNo case conversion is performed on case-insensitive file systems.
\nThe maximum number of symbolic links is platform-independent and generally\n(much) higher than what the native realpath(3) implementation supports.
\nThe callback gets two arguments (err, resolvedPath). May use process.cwd\nto resolve relative paths.
Only paths that can be converted to UTF8 strings are supported.
\nThe optional options argument can be a string specifying an encoding, or an\nobject with an encoding property specifying the character encoding to use for\nthe path passed to the callback. If the encoding is set to 'buffer',\nthe path returned will be passed as a Buffer object.
If path resolves to a socket or a pipe, the function will return a system\ndependent name for that object.
Synchronously computes the canonical pathname by resolving ., .. and\nsymbolic links.
Note that "canonical" does not mean "unique": hard links and bind mounts can\nexpose a file system entity through many pathnames.
\nThis function behaves like realpath(3), with some exceptions:
\nNo case conversion is performed on case-insensitive file systems.
\nThe maximum number of symbolic links is platform-independent and generally\n(much) higher than what the native realpath(3) implementation supports.
\nThe optional options argument can be a string specifying an encoding, or an\nobject with an encoding property specifying the character encoding to use for\nthe returned value. If the encoding is set to 'buffer', the path returned\nwill be passed as a Buffer object.
If path resolves to a socket or a pipe, the function will return a system\ndependent name for that object.
Asynchronously rename file at oldPath to the pathname provided\nas newPath. In the case that newPath already exists, it will\nbe overwritten. No arguments other than a possible exception are\ngiven to the completion callback.
See also: rename(2).
\nfs.rename('oldFile.txt', 'newFile.txt', (err) => {\n if (err) throw err;\n console.log('Rename complete!');\n});\nSynchronous rename(2). Returns undefined.
Asynchronous rmdir(2). No arguments other than a possible exception are given\nto the completion callback.
\nUsing fs.rmdir() on a file (not a directory) results in an ENOENT error on\nWindows and an ENOTDIR error on POSIX.
Synchronous rmdir(2). Returns undefined.
Using fs.rmdirSync() on a file (not a directory) results in an ENOENT error\non Windows and an ENOTDIR error on POSIX.
Asynchronous stat(2). The callback gets two arguments (err, stats) where\nstats is an fs.Stats object.
In case of an error, the err.code will be one of Common System Errors.
Using fs.stat() to check for the existence of a file before calling\nfs.open(), fs.readFile() or fs.writeFile() is not recommended.\nInstead, user code should open/read/write the file directly and handle the\nerror raised if the file is not available.
To check if a file exists without manipulating it afterwards, fs.access()\nis recommended.
Synchronous stat(2).
\n" }, { "textRaw": "fs.symlink(target, path[, type], callback)", "type": "method", "name": "symlink", "meta": { "added": [ "v0.1.31" ], "changes": [ { "version": "v7.6.0", "pr-url": "https://github.com/nodejs/node/pull/10739", "description": "The `target` and `path` parameters can be WHATWG `URL` objects using `file:` protocol. Support is currently still *experimental*." } ] }, "signatures": [ { "params": [ { "textRaw": "`target` {string|Buffer|URL} ", "name": "target", "type": "string|Buffer|URL" }, { "textRaw": "`path` {string|Buffer|URL} ", "name": "path", "type": "string|Buffer|URL" }, { "textRaw": "`type` {string} **Default:** `'file'` ", "name": "type", "type": "string", "default": "`'file'`", "optional": true }, { "textRaw": "`callback` {Function} ", "options": [ { "textRaw": "`err` {Error} ", "name": "err", "type": "Error" } ], "name": "callback", "type": "Function" } ] }, { "params": [ { "name": "target" }, { "name": "path" }, { "name": "type", "optional": true }, { "name": "callback" } ] } ], "desc": "Asynchronous symlink(2). No arguments other than a possible exception are given\nto the completion callback. The type argument can be set to 'dir',\n'file', or 'junction' and is only available on\nWindows (ignored on other platforms). Note that Windows junction points require\nthe destination path to be absolute. When using 'junction', the target\nargument will automatically be normalized to absolute path.
Here is an example below:
\nfs.symlink('./foo', './new-port', callback);\nIt creates a symbolic link named "new-port" that points to "foo".
\n" }, { "textRaw": "fs.symlinkSync(target, path[, type])", "type": "method", "name": "symlinkSync", "meta": { "added": [ "v0.1.31" ], "changes": [ { "version": "v7.6.0", "pr-url": "https://github.com/nodejs/node/pull/10739", "description": "The `target` and `path` parameters can be WHATWG `URL` objects using `file:` protocol. Support is currently still *experimental*." } ] }, "signatures": [ { "params": [ { "textRaw": "`target` {string|Buffer|URL} ", "name": "target", "type": "string|Buffer|URL" }, { "textRaw": "`path` {string|Buffer|URL} ", "name": "path", "type": "string|Buffer|URL" }, { "textRaw": "`type` {string} **Default:** `'file'` ", "name": "type", "type": "string", "default": "`'file'`", "optional": true } ] }, { "params": [ { "name": "target" }, { "name": "path" }, { "name": "type", "optional": true } ] } ], "desc": "Synchronous symlink(2). Returns undefined.
Asynchronous truncate(2). No arguments other than a possible exception are\ngiven to the completion callback. A file descriptor can also be passed as the\nfirst argument. In this case, fs.ftruncate() is called.
Passing a file descriptor is deprecated and may result in an error being thrown\nin the future.
\n" }, { "textRaw": "fs.truncateSync(path[, len])", "type": "method", "name": "truncateSync", "meta": { "added": [ "v0.8.6" ], "changes": [] }, "signatures": [ { "params": [ { "textRaw": "`path` {string|Buffer|URL} ", "name": "path", "type": "string|Buffer|URL" }, { "textRaw": "`len` {integer} **Default:** `0` ", "name": "len", "type": "integer", "default": "`0`", "optional": true } ] }, { "params": [ { "name": "path" }, { "name": "len", "optional": true } ] } ], "desc": "Synchronous truncate(2). Returns undefined. A file descriptor can also be\npassed as the first argument. In this case, fs.ftruncateSync() is called.
Passing a file descriptor is deprecated and may result in an error being thrown\nin the future.
\n" }, { "textRaw": "fs.unlink(path, callback)", "type": "method", "name": "unlink", "meta": { "added": [ "v0.0.2" ], "changes": [ { "version": "REPLACEME", "pr-url": "https://github.com/nodejs/node/pull/12562", "description": "The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime." }, { "version": "v7.6.0", "pr-url": "https://github.com/nodejs/node/pull/10739", "description": "The `path` parameter can be a WHATWG `URL` object using `file:` protocol. Support is currently still *experimental*." }, { "version": "v7.0.0", "pr-url": "https://github.com/nodejs/node/pull/7897", "description": "The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013." } ] }, "signatures": [ { "params": [ { "textRaw": "`path` {string|Buffer|URL} ", "name": "path", "type": "string|Buffer|URL" }, { "textRaw": "`callback` {Function} ", "options": [ { "textRaw": "`err` {Error} ", "name": "err", "type": "Error" } ], "name": "callback", "type": "Function" } ] }, { "params": [ { "name": "path" }, { "name": "callback" } ] } ], "desc": "Asynchronously removes a file or symbolic link. No arguments other than a\npossible exception are given to the completion callback.
\n// Assuming that 'path/file.txt' is a regular file.\nfs.unlink('path/file.txt', (err) => {\n if (err) throw err;\n console.log('path/file.txt was deleted');\n});\nfs.unlink() will not work on a directory, empty or otherwise. To remove a\ndirectory, use fs.rmdir().
See also: unlink(2)
\n" }, { "textRaw": "fs.unlinkSync(path)", "type": "method", "name": "unlinkSync", "meta": { "added": [ "v0.1.21" ], "changes": [ { "version": "v7.6.0", "pr-url": "https://github.com/nodejs/node/pull/10739", "description": "The `path` parameter can be a WHATWG `URL` object using `file:` protocol. Support is currently still *experimental*." } ] }, "signatures": [ { "params": [ { "textRaw": "`path` {string|Buffer|URL} ", "name": "path", "type": "string|Buffer|URL" } ] }, { "params": [ { "name": "path" } ] } ], "desc": "Synchronous unlink(2). Returns undefined.
Stop watching for changes on filename. If listener is specified, only that\nparticular listener is removed. Otherwise, all listeners are removed,\neffectively stopping watching of filename.
Calling fs.unwatchFile() with a filename that is not being watched is a\nno-op, not an error.
Using fs.watch() is more efficient than fs.watchFile() and\nfs.unwatchFile(). fs.watch() should be used instead of fs.watchFile()\nand fs.unwatchFile() when possible.
Change the file system timestamps of the object referenced by path.
The atime and mtime arguments follow these rules:
Dates, or a\nnumeric string like '123456789.0'.NaN, Infinity or\n-Infinity, a Error will be thrown.Synchronous version of fs.utimes(). Returns undefined.
Watch for changes on filename, where filename is either a file or a\ndirectory.
The second argument is optional. If options is provided as a string, it\nspecifies the encoding. Otherwise options should be passed as an object.
The listener callback gets two arguments (eventType, filename). eventType\nis either 'rename' or 'change', and filename is the name of the file\nwhich triggered the event.
Note that on most platforms, 'rename' is emitted whenever a filename appears\nor disappears in the directory.
Also note the listener callback is attached to the 'change' event fired by\nfs.FSWatcher, but it is not the same thing as the 'change' value of\neventType.
The fs.watch API is not 100% consistent across platforms, and is\nunavailable in some situations.
The recursive option is only supported on macOS and Windows.
\n", "miscs": [ { "textRaw": "Availability", "name": "Availability", "type": "misc", "desc": "This feature depends on the underlying operating system providing a way\nto be notified of filesystem changes.
\ninotifykqueuekqueue for files and FSEvents for directories.event ports.ReadDirectoryChangesW.AHAFS, which must be enabled.If the underlying functionality is not available for some reason, then\nfs.watch will not be able to function. For example, watching files or\ndirectories can be unreliable, and in some cases impossible, on network file\nsystems (NFS, SMB, etc), or host file systems when using virtualization software\nsuch as Vagrant, Docker, etc.
It is still possible to use fs.watchFile(), which uses stat polling, but\nthis method is slower and less reliable.
On Linux and macOS systems, fs.watch() resolves the path to an inode and\nwatches the inode. If the watched path is deleted and recreated, it is assigned\na new inode. The watch will emit an event for the delete but will continue\nwatching the original inode. Events for the new inode will not be emitted.\nThis is expected behavior.
AIX files retain the same inode for the lifetime of a file. Saving and closing a\nwatched file on AIX will result in two notifications (one for adding new\ncontent, and one for truncation).
\n" }, { "textRaw": "Filename Argument", "name": "Filename Argument", "type": "misc", "desc": "Providing filename argument in the callback is only supported on Linux,\nmacOS, Windows, and AIX. Even on supported platforms, filename is not always\nguaranteed to be provided. Therefore, don't assume that filename argument is\nalways provided in the callback, and have some fallback logic if it is null.
fs.watch('somedir', (eventType, filename) => {\n console.log(`event type is: ${eventType}`);\n if (filename) {\n console.log(`filename provided: ${filename}`);\n } else {\n console.log('filename not provided');\n }\n});\nWatch for changes on filename. The callback listener will be called each\ntime the file is accessed.
The options argument may be omitted. If provided, it should be an object. The\noptions object may contain a boolean named persistent that indicates\nwhether the process should continue to run as long as files are being watched.\nThe options object may specify an interval property indicating how often the\ntarget should be polled in milliseconds.
The listener gets two arguments the current stat object and the previous\nstat object:
fs.watchFile('message.text', (curr, prev) => {\n console.log(`the current mtime is: ${curr.mtime}`);\n console.log(`the previous mtime was: ${prev.mtime}`);\n});\nThese stat objects are instances of fs.Stat.
To be notified when the file was modified, not just accessed, it is necessary\nto compare curr.mtime and prev.mtime.
When an fs.watchFile operation results in an ENOENT error, it\nwill invoke the listener once, with all the fields zeroed (or, for dates, the\nUnix Epoch). In Windows, blksize and blocks fields will be undefined,\ninstead of zero. If the file is created later on, the listener will be called\nagain, with the latest stat objects. This is a change in functionality since\nv0.10.
Using fs.watch() is more efficient than fs.watchFile and\nfs.unwatchFile. fs.watch should be used instead of fs.watchFile and\nfs.unwatchFile when possible.
When a file being watched by fs.watchFile() disappears and reappears,\nthen the previousStat reported in the second callback event (the file's\nreappearance) will be the same as the previousStat of the first callback\nevent (its disappearance).
This happens when:
\nWrite buffer to the file specified by fd.
offset determines the part of the buffer to be written, and length is\nan integer specifying the number of bytes to write.
position refers to the offset from the beginning of the file where this data\nshould be written. If typeof position !== 'number', the data will be written\nat the current position. See pwrite(2).
The callback will be given three arguments (err, bytesWritten, buffer) where\nbytesWritten specifies how many bytes were written from buffer.
If this method is invoked as its util.promisify()ed version, it returns\na Promise for an object with bytesWritten and buffer properties.
Note that it is unsafe to use fs.write multiple times on the same file\nwithout waiting for the callback. For this scenario,\nfs.createWriteStream is strongly recommended.
On Linux, positional writes don't work when the file is opened in append mode.\nThe kernel ignores the position argument and always appends the data to\nthe end of the file.
\n" }, { "textRaw": "fs.write(fd, string[, position[, encoding]], callback)", "type": "method", "name": "write", "meta": { "added": [ "v0.11.5" ], "changes": [ { "version": "REPLACEME", "pr-url": "https://github.com/nodejs/node/pull/12562", "description": "The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime." }, { "version": "v7.2.0", "pr-url": "https://github.com/nodejs/node/pull/7856", "description": "The `position` parameter is optional now." }, { "version": "v7.0.0", "pr-url": "https://github.com/nodejs/node/pull/7897", "description": "The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013." } ] }, "signatures": [ { "params": [ { "textRaw": "`fd` {integer} ", "name": "fd", "type": "integer" }, { "textRaw": "`string` {string} ", "name": "string", "type": "string" }, { "textRaw": "`position` {integer} ", "name": "position", "type": "integer", "optional": true }, { "textRaw": "`encoding` {string} ", "name": "encoding", "type": "string", "optional": true }, { "textRaw": "`callback` {Function} ", "options": [ { "textRaw": "`err` {Error} ", "name": "err", "type": "Error" }, { "textRaw": "`written` {integer} ", "name": "written", "type": "integer" }, { "textRaw": "`string` {string} ", "name": "string", "type": "string" } ], "name": "callback", "type": "Function" } ] }, { "params": [ { "name": "fd" }, { "name": "string" }, { "name": "position", "optional": true }, { "name": "encoding", "optional": true }, { "name": "callback" } ] } ], "desc": "Write string to the file specified by fd. If string is not a string, then\nthe value will be coerced to one.
position refers to the offset from the beginning of the file where this data\nshould be written. If typeof position !== 'number' the data will be written at\nthe current position. See pwrite(2).
encoding is the expected string encoding.
The callback will receive the arguments (err, written, string) where written\nspecifies how many bytes the passed string required to be written. Note that\nbytes written is not the same as string characters. See Buffer.byteLength.
Unlike when writing buffer, the entire string must be written. No substring\nmay be specified. This is because the byte offset of the resulting data may not\nbe the same as the string offset.
Note that it is unsafe to use fs.write multiple times on the same file\nwithout waiting for the callback. For this scenario,\nfs.createWriteStream is strongly recommended.
On Linux, positional writes don't work when the file is opened in append mode.\nThe kernel ignores the position argument and always appends the data to\nthe end of the file.
\n" }, { "textRaw": "fs.writeFile(file, data[, options], callback)", "type": "method", "name": "writeFile", "meta": { "added": [ "v0.1.29" ], "changes": [ { "version": "REPLACEME", "pr-url": "https://github.com/nodejs/node/pull/12562", "description": "The `callback` parameter is no longer optional. Not passing it will throw a `TypeError` at runtime." }, { "version": "v7.4.0", "pr-url": "https://github.com/nodejs/node/pull/10382", "description": "The `data` parameter can now be a `Uint8Array`." }, { "version": "v7.0.0", "pr-url": "https://github.com/nodejs/node/pull/7897", "description": "The `callback` parameter is no longer optional. Not passing it will emit a deprecation warning with id DEP0013." }, { "version": "v5.0.0", "pr-url": "https://github.com/nodejs/node/pull/3163", "description": "The `file` parameter can be a file descriptor now." } ] }, "signatures": [ { "params": [ { "textRaw": "`file` {string|Buffer|URL|integer} filename or file descriptor ", "name": "file", "type": "string|Buffer|URL|integer", "desc": "filename or file descriptor" }, { "textRaw": "`data` {string|Buffer|Uint8Array} ", "name": "data", "type": "string|Buffer|Uint8Array" }, { "textRaw": "`options` {Object|string} ", "options": [ { "textRaw": "`encoding` {string|null} **Default:** `'utf8'` ", "name": "encoding", "type": "string|null", "default": "`'utf8'`" }, { "textRaw": "`mode` {integer} **Default:** `0o666` ", "name": "mode", "type": "integer", "default": "`0o666`" }, { "textRaw": "`flag` {string} **Default:** `'w'` ", "name": "flag", "type": "string", "default": "`'w'`" } ], "name": "options", "type": "Object|string", "optional": true }, { "textRaw": "`callback` {Function} ", "options": [ { "textRaw": "`err` {Error} ", "name": "err", "type": "Error" } ], "name": "callback", "type": "Function" } ] }, { "params": [ { "name": "file" }, { "name": "data" }, { "name": "options", "optional": true }, { "name": "callback" } ] } ], "desc": "Asynchronously writes data to a file, replacing the file if it already exists.\ndata can be a string or a buffer.
The encoding option is ignored if data is a buffer.
Example:
\nfs.writeFile('message.txt', 'Hello Node.js', (err) => {\n if (err) throw err;\n console.log('The file has been saved!');\n});\nIf options is a string, then it specifies the encoding. Example:
fs.writeFile('message.txt', 'Hello Node.js', 'utf8', callback);\nAny specified file descriptor has to support writing.
\nNote that it is unsafe to use fs.writeFile multiple times on the same file\nwithout waiting for the callback. For this scenario,\nfs.createWriteStream is strongly recommended.
If a file descriptor is specified as the file, it will not be closed\nautomatically.
The synchronous version of fs.writeFile(). Returns undefined.
Synchronous versions of fs.write(). Returns the number of bytes written.
Synchronous versions of fs.write(). Returns the number of bytes written.
Returns an object containing commonly used constants for file system\noperations. The specific constants currently defined are described in\nFS Constants.
\n" } ], "type": "module", "displayName": "fs" } ] }