File I/O is provided by simple wrappers around standard POSIX functions. To\nuse this module do require('fs'). All the methods have asynchronous and\nsynchronous forms.
The 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.
When using the synchronous form any exceptions are immediately thrown.\nExceptions may be handled using try/catch, or they may be allowed to\nbubble up.
Here is an example of the asynchronous version:
\nconst fs = require('fs');\n\nfs.unlink('/tmp/hello', (err) => {\n if (err) throw err;\n console.log('successfully deleted /tmp/hello');\n});\nHere is the synchronous version:
\nconst fs = require('fs');\n\nfs.unlinkSync('/tmp/hello');\nconsole.log('successfully deleted /tmp/hello');\nWith the asynchronous methods there is no guaranteed ordering. So the\nfollowing is prone to error:
\nfs.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});\nIt could be that fs.stat is executed before fs.rename.\nThe correct way to do this is to chain the callbacks.
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: ${JSON.stringify(stats)}`);\n });\n});\nIn busy processes, the programmer is strongly encouraged to use the\nasynchronous versions of these calls. The synchronous versions will block\nthe entire process until they complete--halting all connections.
\nThe relative path to a filename can be used. Remember, however, that this path\nwill be relative to process.cwd().
While it is not recommended, most fs functions allow the callback argument to\nbe omitted, in which case a default callback is used that rethrows errors. To\nget a trace to the original call site, set the NODE_DEBUG environment\nvariable:
Note: Omitting the callback function on asynchronous fs functions is\ndeprecated and may result in an error being thrown in the future.
\n$ 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.>\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 { URL } = require('url');\nconst fileUrl = new URL('file:///tmp/hello');\n\nfs.readFileSync(fileUrl);\nNote: file: 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\nNote: file: 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 */\nfs functions support passing and receiving paths as both strings\nand Buffers. The latter is intended to make it possible to work with\nfilesystems that allow for non-UTF-8 filenames. For most typical\nuses, working with paths as Buffers will be unnecessary, as the string\nAPI converts to and from UTF-8 automatically.
Note: On certain file systems (such as NTFS and HFS+) filenames\nwill always be encoded as UTF-8. On such file systems, passing\nnon-UTF-8 encoded Buffers to fs functions will not work as expected.
The following constants are exported by fs.constants.
Note: 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.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 synchronous I/O. | \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
Objects returned from fs.watch() are of this type.
The listener callback provided to fs.watch() receives the returned FSWatcher's\nchange events.
The object itself emits these events:
\n", "events": [ { "textRaw": "Event: 'change'", "type": "event", "name": "change", "meta": { "added": [ "v0.5.8" ], "changes": [] }, "params": [], "desc": "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 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});\nEmitted when an error occurs.
\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.
ReadStream is a Readable Stream.
Emitted when the ReadStream's underlying file descriptor has been closed\nusing the fs.close() method.
Emitted when the ReadStream's file is opened.
\n" } ], "properties": [ { "textRaw": "readStream.bytesRead", "name": "bytesRead", "meta": { "added": [ "6.4.0" ], "changes": [] }, "desc": "The number of bytes read so far.
\n" }, { "textRaw": "readStream.path", "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.
Objects returned from fs.stat(), fs.lstat() and fs.fstat() and\ntheir synchronous counterparts are of this type.
stats.isFile()stats.isDirectory()stats.isBlockDevice()stats.isCharacterDevice()stats.isSymbolicLink() (only valid with fs.lstat())stats.isFIFO()stats.isSocket()For a regular file util.inspect(stats) would return a string very\nsimilar to this:
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 }\nNote: atimeMs, mtimeMs, ctimeMs, birthtimeMs are numbers\nthat hold the corresponding times in milliseconds. Their precision is platform\nspecific. atime, mtime, ctime, and birthtime are Date\nobject alternate representations of the various times. The Date and number\nvalues are not connected. Assigning a new number value, or mutating the Date\nvalue, will not be reflected in the corresponding alternate representation.
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 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\nusing the fs.close() method.
Emitted when the WriteStream's file is opened.
\n" } ], "properties": [ { "textRaw": "writeStream.bytesWritten", "name": "bytesWritten", "meta": { "added": [ "v0.4.7" ], "changes": [] }, "desc": "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.
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 populated. 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.
For example:
\nwrite (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 won’t 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} ", "name": "mode", "type": "integer", "optional": true } ] }, { "params": [ { "name": "path" }, { "name": "mode", "optional": true } ] } ], "desc": "Synchronous version of fs.access(). This throws if any accessibility\nchecks fail, and does nothing otherwise.
Asynchronously append data to a file, creating the file if it does not yet exist.\ndata 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);\nAny specified file descriptor has to have been opened for appending.
\nNote: If a file descriptor is specified as the file, it will not be closed\nautomatically.
The synchronous version of fs.appendFile(). Returns undefined.
Asynchronous chmod(2). No arguments other than a possible exception are given\nto the completion callback.
\n" }, { "textRaw": "fs.chmodSync(path, mode)", "type": "method", "name": "chmodSync", "meta": { "added": [ "v0.6.7" ], "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} ", "name": "mode", "type": "integer" } ] }, { "params": [ { "name": "path" }, { "name": "mode" } ] } ], "desc": "Synchronous chmod(2). Returns undefined.
Asynchronous chown(2). No arguments other than a possible exception are given\nto the completion callback.
\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": "Synchronous chown(2). Returns undefined.
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.
Returns a new ReadStream object. (See Readable Stream).
Be 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 is an object or string with the following defaults:
const defaults = {\n flags: 'r',\n encoding: null,\n fd: null,\n mode: 0o666,\n autoClose: true\n};\noptions 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.
Returns a new WriteStream object. (See Writable Stream).
options is an object or string with the following defaults:
const defaults = {\n flags: 'w',\n defaultEncoding: 'utf8',\n fd: null,\n mode: 0o666,\n autoClose: true\n};\noptions 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 defaultEncoding can be any one of those accepted by\nBuffer.
If autoClose is set to true (default behavior) on error or end\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.
For example:
\nwrite (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 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": [ { "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 file 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). Returns an instance of fs.Stats.
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', 'utf-8'));\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", "desc": "default = `0`" } ] }, { "params": [ { "name": "fd" }, { "name": "len" } ] } ], "desc": "Synchronous ftruncate(2). Returns undefined.
Change the file timestamps of a file referenced by the supplied file\ndescriptor.
\n" }, { "textRaw": "fs.futimesSync(fd, atime, mtime)", "type": "method", "name": "futimesSync", "meta": { "added": [ "v0.4.2" ], "changes": [ { "version": "v4.1.0", "pr-url": "https://github.com/nodejs/node/pull/2387", "description": "Numeric strings, `NaN` and `Infinity` are now allowed time specifiers." } ] }, "signatures": [ { "params": [ { "textRaw": "`fd` {integer} ", "name": "fd", "type": "integer" }, { "textRaw": "`atime` {integer} ", "name": "atime", "type": "integer" }, { "textRaw": "`mtime` {integer} ", "name": "mtime", "type": "integer" } ] }, { "params": [ { "name": "fd" }, { "name": "atime" }, { "name": "mtime" } ] } ], "desc": "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} ", "name": "path", "type": "string|Buffer" }, { "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} ", "name": "path", "type": "string|Buffer" }, { "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). Returns an instance of fs.Stats.
Asynchronous mkdir(2). No arguments other than a possible exception are given\nto the completion callback. mode defaults to 0o777.
Synchronous mkdir(2). Returns undefined.
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('/tmp/foo-', (err, folder) => {\n if (err) throw err;\n console.log(folder);\n // Prints: /tmp/foo-itXde2\n});\nNote: The fs.mkdtemp() method will append the six randomly selected\ncharacters directly to the prefix string. For instance, given a directory\n/tmp, if the intention is to create a temporary directory within /tmp,\nthe prefix must end with a trailing platform-specific path separator\n(require('path').sep).
// The parent directory for the new temporary directory\nconst tmpDir = '/tmp';\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.
'a+' - Open file for reading and appending.\nThe file is created if it does not exist.
'ax+' - Like 'a+' but fails if path exists.
mode sets the file mode (permission and sticky bits), but only if the file was\ncreated. It defaults to 0666, readable and writable.
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.
\nNote: The behavior of fs.open() is platform-specific for some flags. As\nsuch, opening 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});\nSynchronous 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 integer specifying where to begin reading from in the file.\nIf position is null, data will be read from the current file position.
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). Returns an array of filenames excluding '.' and\n'..'.
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.
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);\nNote: When the path is a directory, the behavior of\nfs.readFile() and fs.readFileSync() is platform-specific. On macOS,\nLinux, and Windows, an error will be returned. On FreeBSD, a representation\nof the directory's contents will 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.
\nNote: If a file descriptor is specified as the path, it will not be closed\nautomatically.
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.
Note: Similar to fs.readFile(), when the path is a directory, the\nbehavior of fs.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.
Asynchronous realpath(3). The callback gets two arguments (err,\nresolvedPath). May use process.cwd to 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.
Note: If path resolves to a socket or a pipe, the function will return a\nsystem dependent name for that object.
Synchronous realpath(3). Returns the resolved path.
\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 returned value. If the encoding is set to 'buffer', the path returned\nwill be passed as a Buffer object.
Note: If path resolves to a socket or a pipe, the function will return a\nsystem dependent name for that object.
Asynchronous rename(2). No arguments other than a possible exception are given\nto the completion callback.
\n" }, { "textRaw": "fs.renameSync(oldPath, newPath)", "type": "method", "name": "renameSync", "meta": { "added": [ "v0.1.21" ], "changes": [ { "version": "v7.6.0", "pr-url": "https://github.com/nodejs/node/pull/10739", "description": "The `oldPath` and `newPath` parameters can be WHATWG `URL` objects using `file:` protocol. Support is currently still *experimental*." } ] }, "signatures": [ { "params": [ { "textRaw": "`oldPath` {string|Buffer|URL} ", "name": "oldPath", "type": "string|Buffer|URL" }, { "textRaw": "`newPath` {string|Buffer|URL} ", "name": "newPath", "type": "string|Buffer|URL" } ] }, { "params": [ { "name": "oldPath" }, { "name": "newPath" } ] } ], "desc": "Synchronous rename(2). Returns undefined.
Asynchronous rmdir(2). No arguments other than a possible exception are given\nto the completion callback.
\n" }, { "textRaw": "fs.rmdirSync(path)", "type": "method", "name": "rmdirSync", "meta": { "added": [ "v0.1.21" ], "changes": [ { "version": "v7.6.0", "pr-url": "https://github.com/nodejs/node/pull/10739", "description": "The `path` parameters 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 rmdir(2). Returns undefined.
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). Returns an instance of fs.Stats.
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' (default is 'file') 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} ", "name": "type", "type": "string", "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.
Synchronous truncate(2). Returns undefined. A file descriptor can also be\npassed as the first argument. In this case, fs.ftruncateSync() is called.
Asynchronous unlink(2). No arguments other than a possible exception are given\nto the completion callback.
\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.
Note: 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 file timestamps of the file referenced by the supplied path.
\nNote: The arguments atime and mtime of the following related functions\nfollow these rules:
Date.now()\nreturns milliseconds, so it should be divided by 1000 before passing it in.'123456789', the value will get\nconverted to the corresponding number.NaN, Infinity or -Infinity, an 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 returned object is a fs.FSWatcher.
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 is either\n'rename' or 'change', and filename is the name of the file which triggered\nthe 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.
In AIX, save and close of a file being watched causes two notifications -\none for adding new content, and one for truncation. Moreover, save and\nclose operations on some platforms cause inode changes that force watch\noperations to become invalid and ineffective. AIX retains inode for the\nlifetime of a file, that way though this is different from Linux / macOS,\nthis improves the usability of file watching. This is expected behavior.
\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 default is\n{ persistent: true, interval: 5007 }.
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.
Note: 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.
Note: 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.
Write 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": "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." } ] }, "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} ", "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": "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." }, { "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|integer} filename or file descriptor ", "name": "file", "type": "string|Buffer|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", "desc": "default = `'utf8'`" }, { "textRaw": "`mode` {integer} default = `0o666` ", "name": "mode", "type": "integer", "desc": "default = `0o666`" }, { "textRaw": "`flag` {string} default = `'w'` ", "name": "flag", "type": "string", "desc": "default = `'w'`" } ], "name": "options", "type": "Object|string", "optional": true }, { "textRaw": "`callback` {Function} ", "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. It defaults\nto 'utf8'.
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.
Note: 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" } ] }