{ "type": "module", "source": "doc/api/esm.md", "introduced_in": "v8.5.0", "stability": 1, "stabilityText": "Experimental", "properties": [ { "textRaw": "`meta` {Object}", "type": "Object", "name": "meta", "desc": "

The import.meta metaproperty is an Object that contains the following\nproperty:

\n" } ], "miscs": [ { "textRaw": "ECMAScript Modules", "name": "ECMAScript Modules", "introduced_in": "v8.5.0", "type": "misc", "stability": 1, "stabilityText": "Experimental", "miscs": [ { "textRaw": "Introduction", "name": "esm", "desc": "

ECMAScript modules are the official standard format to package JavaScript\ncode for reuse. Modules are defined using a variety of import and\nexport statements.

\n

Node.js fully supports ECMAScript modules as they are currently specified and\nprovides limited interoperability between them and the existing module format,\nCommonJS.

\n

Node.js contains support for ES Modules based upon the\nNode.js EP for ES Modules and the ECMAScript-modules implementation.

\n

Expect major changes in the implementation including interoperability support,\nspecifier resolution, and default behavior.

", "type": "misc", "displayName": "esm" }, { "textRaw": "Enabling", "name": "Enabling", "type": "misc", "desc": "

The --experimental-modules flag can be used to enable support for\nECMAScript modules (ES modules).

\n

Once enabled, Node.js will treat the following as ES modules when passed to\nnode as the initial input, or when referenced by import statements within\nES module code:

\n\n

Node.js will treat as CommonJS all other forms of input, such as .js files\nwhere the nearest parent package.json file contains no top-level \"type\"\nfield, or string input without the flag --input-type. This behavior is to\npreserve backward compatibility. However, now that Node.js supports both\nCommonJS and ES modules, it is best to be explicit whenever possible. Node.js\nwill treat the following as CommonJS when passed to node as the initial input,\nor when referenced by import statements within ES module code:

\n" }, { "textRaw": "package.json \"type\" field", "name": "package.json_\"type\"_field", "desc": "

Files ending with .js or .mjs, or lacking any extension,\nwill be loaded as ES modules when the nearest parent package.json file\ncontains a top-level field \"type\" with a value of \"module\".

\n

The nearest parent package.json is defined as the first package.json found\nwhen searching in the current folder, that folder’s parent, and so on up\nuntil the root of the volume is reached.

\n\n
// package.json\n{\n  \"type\": \"module\"\n}\n
\n
# In same folder as above package.json\nnode --experimental-modules my-app.js # Runs as ES module\n
\n

If the nearest parent package.json lacks a \"type\" field, or contains\n\"type\": \"commonjs\", extensionless and .js files are treated as CommonJS.\nIf the volume root is reached and no package.json is found,\nNode.js defers to the default, a package.json with no \"type\"\nfield.

\n

import statements of .js and extensionless files are treated as ES modules\nif the nearest parent package.json contains \"type\": \"module\".

\n
// my-app.js, part of the same example as above\nimport './startup.js'; // Loaded as ES module because of package.json\n
", "type": "misc", "displayName": "package.json \"type\" field" }, { "textRaw": "Package Scope and File Extensions", "name": "package_scope_and_file_extensions", "desc": "

A folder containing a package.json file, and all subfolders below that\nfolder down until the next folder containing another package.json, is\nconsidered a package scope. The \"type\" field defines how .js and\nextensionless files should be treated within a particular package.json file’s\npackage scope. Every package in a project’s node_modules folder contains its\nown package.json file, so each project’s dependencies have their own package\nscopes. A package.json lacking a \"type\" field is treated as if it contained\n\"type\": \"commonjs\".

\n

The package scope applies not only to initial entry points (node --experimental-modules my-app.js) but also to files referenced by import\nstatements and import() expressions.

\n
// my-app.js, in an ES module package scope because there is a package.json\n// file in the same folder with \"type\": \"module\".\n\nimport './startup/init.js';\n// Loaded as ES module since ./startup contains no package.json file,\n// and therefore inherits the ES module package scope from one level up.\n\nimport 'commonjs-package';\n// Loaded as CommonJS since ./node_modules/commonjs-package/package.json\n// lacks a \"type\" field or contains \"type\": \"commonjs\".\n\nimport './node_modules/commonjs-package/index.js';\n// Loaded as CommonJS since ./node_modules/commonjs-package/package.json\n// lacks a \"type\" field or contains \"type\": \"commonjs\".\n
\n

Files ending with .mjs are always loaded as ES modules regardless of package\nscope.

\n

Files ending with .cjs are always loaded as CommonJS regardless of package\nscope.

\n
import './legacy-file.cjs';\n// Loaded as CommonJS since .cjs is always loaded as CommonJS.\n\nimport 'commonjs-package/src/index.mjs';\n// Loaded as ES module since .mjs is always loaded as ES module.\n
\n

The .mjs and .cjs extensions may be used to mix types within the same\npackage scope:

\n", "type": "misc", "displayName": "Package Scope and File Extensions" }, { "textRaw": "--input-type flag", "name": "--input-type_flag", "desc": "

Strings passed in as an argument to --eval or --print (or -e or -p), or\npiped to node via STDIN, will be treated as ES modules when the\n--input-type=module flag is set.

\n
node --experimental-modules --input-type=module --eval \\\n  \"import { sep } from 'path'; console.log(sep);\"\n\necho \"import { sep } from 'path'; console.log(sep);\" | \\\n  node --experimental-modules --input-type=module\n
\n

For completeness there is also --input-type=commonjs, for explicitly running\nstring input as CommonJS. This is the default behavior if --input-type is\nunspecified.

", "type": "misc", "displayName": "--input-type flag" }, { "textRaw": "Package Entry Points", "name": "package_entry_points", "desc": "

The package.json \"main\" field defines the entry point for a package,\nwhether the package is included into CommonJS via require or into an ES\nmodule via import.

\n\n
// ./node_modules/es-module-package/package.json\n{\n  \"type\": \"module\",\n  \"main\": \"./src/index.js\"\n}\n
\n
// ./my-app.mjs\n\nimport { something } from 'es-module-package';\n// Loads from ./node_modules/es-module-package/src/index.js\n
\n

An attempt to require the above es-module-package would attempt to load\n./node_modules/es-module-package/src/index.js as CommonJS, which would throw\nan error as Node.js would not be able to parse the export statement in\nCommonJS.

\n

As with import statements, for ES module usage the value of \"main\" must be\na full path including extension: \"./index.mjs\", not \"./index\".

\n

If the package.json \"type\" field is omitted, a .js file in \"main\" will\nbe interpreted as CommonJS.

\n
\n

Currently a package can define either a CommonJS entry point or an ES\nmodule entry point; there is no way to specify separate entry points for\nCommonJS and ES module usage. This means that a package entry point can be\nincluded via require or via import but not both.

\n

Such a limitation makes it difficult for packages to support both new versions\nof Node.js that understand ES modules and older versions of Node.js that\nunderstand only CommonJS. There is work ongoing to remove this limitation, and\nit will very likely entail changes to the behavior of \"main\" as defined\nhere.

\n
", "type": "misc", "displayName": "Package Entry Points" }, { "textRaw": "import Specifiers", "name": "import_specifiers", "modules": [ { "textRaw": "Terminology", "name": "terminology", "desc": "

The specifier of an import statement is the string after the from keyword,\ne.g. 'path' in import { sep } from 'path'. Specifiers are also used in\nexport from statements, and as the argument to an import() expression.

\n

There are four types of specifiers:

\n\n

Bare specifiers, and the bare specifier portion of deep import specifiers, are\nstrings; but everything else in a specifier is a URL.

\n

Only file:// URLs are supported. A specifier like\n'https://example.com/app.js' may be supported by browsers but it is not\nsupported in Node.js.

\n

Specifiers may not begin with / or //. These are reserved for potential\nfuture use. The root of the current volume may be referenced via file:///.

", "type": "module", "displayName": "Terminology" } ], "type": "misc", "displayName": "import Specifiers" }, { "textRaw": "Differences Between ES Modules and CommonJS", "name": "differences_between_es_modules_and_commonjs", "modules": [ { "textRaw": "Mandatory file extensions", "name": "mandatory_file_extensions", "desc": "

A file extension must be provided when using the import keyword. Directory\nindexes (e.g. './startup/index.js') must also be fully specified.

\n

This behavior matches how import behaves in browser environments, assuming a\ntypically configured server.

", "type": "module", "displayName": "Mandatory file extensions" }, { "textRaw": "No NODE_PATH", "name": "no_node_path", "desc": "

NODE_PATH is not part of resolving import specifiers. Please use symlinks\nif this behavior is desired.

", "type": "module", "displayName": "No NODE_PATH" }, { "textRaw": "No require, exports, module.exports, __filename, __dirname", "name": "no_require,_exports,_module.exports,___filename,___dirname", "desc": "

These CommonJS variables are not available in ES modules.

\n

require can be imported into an ES module using module.createRequire().

\n

An equivalent for __filename and __dirname is import.meta.url.

", "type": "module", "displayName": "No require, exports, module.exports, __filename, __dirname" }, { "textRaw": "No require.extensions", "name": "no_require.extensions", "desc": "

require.extensions is not used by import. The expectation is that loader\nhooks can provide this workflow in the future.

", "type": "module", "displayName": "No require.extensions" }, { "textRaw": "No require.cache", "name": "no_require.cache", "desc": "

require.cache is not used by import. It has a separate cache.

", "type": "module", "displayName": "No require.cache" }, { "textRaw": "URL-based paths", "name": "url-based_paths", "desc": "

ES modules are resolved and cached based upon\nURL semantics. This means that files containing\nspecial characters such as # and ? need to be escaped.

\n

Modules will be loaded multiple times if the import specifier used to resolve\nthem have a different query or fragment.

\n
import './foo.mjs?query=1'; // loads ./foo.mjs with query of \"?query=1\"\nimport './foo.mjs?query=2'; // loads ./foo.mjs with query of \"?query=2\"\n
\n

For now, only modules using the file: protocol can be loaded.

", "type": "module", "displayName": "URL-based paths" } ], "type": "misc", "displayName": "Differences Between ES Modules and CommonJS" }, { "textRaw": "Interoperability with CommonJS", "name": "interoperability_with_commonjs", "modules": [ { "textRaw": "require", "name": "require", "desc": "

require always treats the files it references as CommonJS. This applies\nwhether require is used the traditional way within a CommonJS environment, or\nin an ES module environment using module.createRequire().

\n

To include an ES module into CommonJS, use import().

", "type": "module", "displayName": "require" }, { "textRaw": "import statements", "name": "import_statements", "desc": "

An import statement can reference either ES module or CommonJS JavaScript.\nOther file types such as JSON and Native modules are not supported. For those,\nuse module.createRequire().

\n

import statements are permitted only in ES modules. For similar functionality\nin CommonJS, see import().

\n

The specifier of an import statement (the string after the from keyword)\ncan either be an URL-style relative path like './file.mjs' or a package name\nlike 'fs'.

\n

Like in CommonJS, files within packages can be accessed by appending a path to\nthe package name.

\n
import { sin, cos } from 'geometry/trigonometry-functions.mjs';\n
\n
\n

Currently only the “default export” is supported for CommonJS files or\npackages:

\n\n
import packageMain from 'commonjs-package'; // Works\n\nimport { method } from 'commonjs-package'; // Errors\n
\n

There are ongoing efforts to make the latter code possible.

\n
", "type": "module", "displayName": "import statements" }, { "textRaw": "import() expressions", "name": "import()_expressions", "desc": "

Dynamic import() is supported in both CommonJS and ES modules. It can be used\nto include ES module files from CommonJS code.

\n
(async () => {\n  await import('./my-app.mjs');\n})();\n
", "type": "module", "displayName": "import() expressions" } ], "type": "misc", "displayName": "Interoperability with CommonJS" }, { "textRaw": "CommonJS, JSON, and Native Modules", "name": "commonjs,_json,_and_native_modules", "desc": "

CommonJS, JSON, and Native modules can be used with\nmodule.createRequire().

\n
// cjs.js\nmodule.exports = 'cjs';\n\n// esm.mjs\nimport { createRequire } from 'module';\nimport { fileURLToPath as fromURL } from 'url';\n\nconst require = createRequire(fromURL(import.meta.url));\n\nconst cjs = require('./cjs');\ncjs === 'cjs'; // true\n
", "type": "misc", "displayName": "CommonJS, JSON, and Native Modules" }, { "textRaw": "Builtin modules", "name": "builtin_modules", "desc": "

Builtin modules will provide named exports of their public API, as well as a\ndefault export which can be used for, among other things, modifying the named\nexports. Named exports of builtin modules are updated when the corresponding\nexports property is accessed, redefined, or deleted.

\n
import EventEmitter from 'events';\nconst e = new EventEmitter();\n
\n
import { readFile } from 'fs';\nreadFile('./foo.txt', (err, source) => {\n  if (err) {\n    console.error(err);\n  } else {\n    console.log(source);\n  }\n});\n
\n
import fs, { readFileSync } from 'fs';\n\nfs.readFileSync = () => Buffer.from('Hello, ESM');\n\nfs.readFileSync === readFileSync;\n
", "type": "misc", "displayName": "Builtin modules" }, { "textRaw": "Experimental JSON Modules", "name": "experimental_json_modules", "desc": "

Note: This API is still being designed and is subject to change.

\n

Currently importing JSON modules are only supported in the commonjs mode\nand are loaded using the CJS loader. WHATWG JSON modules are currently\nbeing standardized, and are experimentally supported by including the\nadditional flag --experimental-json-modules when running Node.js.

\n

When the --experimental-json-modules flag is included both the\ncommonjs and module mode will use the new experimental JSON\nloader. The imported JSON only exposes a default, there is no\nsupport for named exports. A cache entry is created in the CommonJS\ncache, to avoid duplication. The same object will be returned in\nCommonJS if the JSON module has already been imported from the\nsame path.

\n

Assuming an index.mjs with

\n\n
import packageConfig from './package.json';\n
\n

The --experimental-json-modules flag is needed for the module\nto work.

\n
node --experimental-modules index.mjs # fails\nnode --experimental-modules --experimental-json-modules index.mjs # works\n
", "type": "misc", "displayName": "Experimental JSON Modules" }, { "textRaw": "Experimental Wasm Modules", "name": "experimental_wasm_modules", "desc": "

Importing Web Assembly modules is supported under the\n--experimental-wasm-modules flag, allowing any .wasm files to be\nimported as normal modules while also supporting their module imports.

\n

This integration is in line with the\nES Module Integration Proposal for Web Assembly.

\n

For example, an index.mjs containing:

\n
import * as M from './module.wasm';\nconsole.log(M);\n
\n

executed under:

\n
node --experimental-modules --experimental-wasm-modules index.mjs\n
\n

would provide the exports interface for the instantiation of module.wasm.

", "type": "misc", "displayName": "Experimental Wasm Modules" }, { "textRaw": "Experimental Loader hooks", "name": "Experimental Loader hooks", "type": "misc", "desc": "

Note: This API is currently being redesigned and will still change.

\n

To customize the default module resolution, loader hooks can optionally be\nprovided via a --loader ./loader-name.mjs argument to Node.js.

\n

When hooks are used they only apply to ES module loading and not to any\nCommonJS modules loaded.

", "miscs": [ { "textRaw": "Resolve hook", "name": "resolve_hook", "desc": "

The resolve hook returns the resolved file URL and module format for a\ngiven module specifier and parent file URL:

\n
const baseURL = new URL('file://');\nbaseURL.pathname = `${process.cwd()}/`;\n\nexport async function resolve(specifier,\n                              parentModuleURL = baseURL,\n                              defaultResolver) {\n  return {\n    url: new URL(specifier, parentModuleURL).href,\n    format: 'module'\n  };\n}\n
\n

The parentModuleURL is provided as undefined when performing main Node.js\nload itself.

\n

The default Node.js ES module resolution function is provided as a third\nargument to the resolver for easy compatibility workflows.

\n

In addition to returning the resolved file URL value, the resolve hook also\nreturns a format property specifying the module format of the resolved\nmodule. This can be one of the following:

\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
formatDescription
'builtin'Load a Node.js builtin module
'commonjs'Load a Node.js CommonJS module
'dynamic'Use a dynamic instantiate hook
'json'Load a JSON file
'module'Load a standard JavaScript module
'wasm'Load a WebAssembly module
\n

For example, a dummy loader to load JavaScript restricted to browser resolution\nrules with only JS file extension and Node.js builtin modules support could\nbe written:

\n
import path from 'path';\nimport process from 'process';\nimport Module from 'module';\n\nconst builtins = Module.builtinModules;\nconst JS_EXTENSIONS = new Set(['.js', '.mjs']);\n\nconst baseURL = new URL('file://');\nbaseURL.pathname = `${process.cwd()}/`;\n\nexport function resolve(specifier, parentModuleURL = baseURL, defaultResolve) {\n  if (builtins.includes(specifier)) {\n    return {\n      url: specifier,\n      format: 'builtin'\n    };\n  }\n  if (/^\\.{0,2}[/]/.test(specifier) !== true && !specifier.startsWith('file:')) {\n    // For node_modules support:\n    // return defaultResolve(specifier, parentModuleURL);\n    throw new Error(\n      `imports must begin with '/', './', or '../'; '${specifier}' does not`);\n  }\n  const resolved = new URL(specifier, parentModuleURL);\n  const ext = path.extname(resolved.pathname);\n  if (!JS_EXTENSIONS.has(ext)) {\n    throw new Error(\n      `Cannot load file with non-JavaScript file extension ${ext}.`);\n  }\n  return {\n    url: resolved.href,\n    format: 'module'\n  };\n}\n
\n

With this loader, running:

\n
NODE_OPTIONS='--experimental-modules --loader ./custom-loader.mjs' node x.js\n
\n

would load the module x.js as an ES module with relative resolution support\n(with node_modules loading skipped in this example).

", "type": "misc", "displayName": "Resolve hook" }, { "textRaw": "Dynamic instantiate hook", "name": "dynamic_instantiate_hook", "desc": "

To create a custom dynamic module that doesn't correspond to one of the\nexisting format interpretations, the dynamicInstantiate hook can be used.\nThis hook is called only for modules that return format: 'dynamic' from\nthe resolve hook.

\n
export async function dynamicInstantiate(url) {\n  return {\n    exports: ['customExportName'],\n    execute: (exports) => {\n      // Get and set functions provided for pre-allocated export names\n      exports.customExportName.set('value');\n    }\n  };\n}\n
\n

With the list of module exports provided upfront, the execute function will\nthen be called at the exact point of module evaluation order for that module\nin the import tree.

", "type": "misc", "displayName": "Dynamic instantiate hook" } ] }, { "textRaw": "Resolution Algorithm", "name": "resolution_algorithm", "modules": [ { "textRaw": "Features", "name": "features", "desc": "

The resolver has the following properties:

\n", "type": "module", "displayName": "Features" }, { "textRaw": "Resolver Algorithm", "name": "resolver_algorithm", "desc": "

The algorithm to load an ES module specifier is given through the\nESM_RESOLVE method below. It returns the resolved URL for a\nmodule specifier relative to a parentURL, in addition to the unique module\nformat for that resolved URL given by the ESM_FORMAT routine.

\n

The \"module\" format is returned for an ECMAScript Module, while the\n\"commonjs\" format is used to indicate loading through the legacy\nCommonJS loader. Additional formats such as \"addon\" can be extended in future\nupdates.

\n

In the following algorithms, all subroutine errors are propagated as errors\nof these top-level routines.

\n

isMain is true when resolving the Node.js application entry point.

\n
\nResolver algorithm specification\n

ESMRESOLVE(_specifier, parentURL, isMain)

\n
\n
    \n
  1. Let resolvedURL be undefined.
    2. \n
  2. \n

    If specifier is a valid URL, then

    \n
      \n
    1. Set resolvedURL to the result of parsing and reserializing\nspecifier as a URL.
      2. \n
    \n
    3. \n
  3. \n

    Otherwise, if specifier starts with \"/\", then

    \n
      \n
    1. Throw an Invalid Specifier error.
      2. \n
    \n
    4. \n
  4. \n

    Otherwise, if specifier starts with \"./\" or \"../\", then

    \n
      \n
    1. Set resolvedURL to the URL resolution of specifier relative to\nparentURL.
      2. \n
    \n
    5. \n
  5. \n

    Otherwise,

    \n
      \n
    1. Note: specifier is now a bare specifier.
      2. \n
    2. Set resolvedURL the result of\nPACKAGE_RESOLVE(specifier, parentURL).
      3. \n
    \n
    6. \n
  6. \n

    If the file at resolvedURL does not exist, then

    \n
      \n
    1. Throw a Module Not Found error.
      2. \n
    \n
    7. \n
  7. Set resolvedURL to the real path of resolvedURL.
    8. \n
  8. Let format be the result of ESM_FORMAT(resolvedURL, isMain).
    9. \n
  9. Load resolvedURL as module format, format.
    10. \n
\n
\n

PACKAGERESOLVE(_packageSpecifier, parentURL)

\n
\n
    \n
  1. Let packageName be undefined.
    2. \n
  2. Let packageSubpath be undefined.
    3. \n
  3. \n

    If packageSpecifier is an empty string, then

    \n
      \n
    1. Throw an Invalid Specifier error.
      2. \n
    \n
    4. \n
  4. \n

    If packageSpecifier does not start with \"@\", then

    \n
      \n
    1. Set packageName to the substring of packageSpecifier until the\nfirst \"/\" separator or the end of the string.
      2. \n
    \n
    5. \n
  5. \n

    Otherwise,

    \n
      \n
    1. \n

      If packageSpecifier does not contain a \"/\" separator, then

      \n
        \n
      1. Throw an Invalid Specifier error.
        2. \n
      \n
      2. \n
    2. Set packageName to the substring of packageSpecifier\nuntil the second \"/\" separator or the end of the string.
      3. \n
    \n
    6. \n
  6. Let packageSubpath be the substring of packageSpecifier from the\nposition at the length of packageName plus one, if any.
    7. \n
  7. Assert: packageName is a valid package name or scoped package name.
    8. \n
  8. Assert: packageSubpath is either empty, or a path without a leading\nseparator.
    9. \n
  9. \n

    If packageSubpath contains any \".\" or \"..\" segments or percent\nencoded strings for \"/\" or \"\\\" then,

    \n
      \n
    1. Throw an Invalid Specifier error.
      2. \n
    \n
    10. \n
  10. \n

    If packageSubpath is empty and packageName is a Node.js builtin\nmodule, then

    \n
      \n
    1. Return the string \"node:\" concatenated with packageSpecifier.
      2. \n
    \n
    11. \n
  11. \n

    While parentURL is not the file system root,

    \n
      \n
    1. Let packageURL be the URL resolution of \"nodemodules/\"\nconcatenated with _packageSpecifier, relative to parentURL.
      2. \n
    2. Set parentURL to the parent folder URL of parentURL.
      3. \n
    3. \n

      If the folder at packageURL does not exist, then

      \n
        \n
      1. Set parentURL to the parent URL path of parentURL.
        2. \n
      2. Continue the next loop iteration.
        3. \n
      \n
      4. \n
    4. Let pjson be the result of READ_PACKAGE_JSON(packageURL).
      5. \n
    5. \n

      If packageSubpath is empty, then

      \n
        \n
      1. Return the result of PACKAGE_MAIN_RESOLVE(packageURL,\npjson).
        2. \n
      \n
      6. \n
    6. \n

      Otherwise,

      \n
        \n
      1. Return the URL resolution of packageSubpath in packageURL.
        2. \n
      \n
      7. \n
    \n
    12. \n
  12. Throw a Module Not Found error.
    13. \n
\n
\n

PACKAGEMAIN_RESOLVE(_packageURL, pjson)

\n
\n
    \n
  1. \n

    If pjson is null, then

    \n
      \n
    1. Throw a Module Not Found error.
      2. \n
    \n
    2. \n
  2. \n

    If pjson.main is a String, then

    \n
      \n
    1. Let resolvedMain be the concatenation of packageURL, \"/\", and\npjson.main.
      2. \n
    2. \n

      If the file at resolvedMain exists, then

      \n
        \n
      1. Return resolvedMain.
        2. \n
      \n
      3. \n
    \n
    3. \n
  3. \n

    If pjson.type is equal to \"module\", then

    \n
      \n
    1. Throw a Module Not Found error.
      2. \n
    \n
    4. \n
  4. Let legacyMainURL be the result applying the legacy\nLOAD_AS_DIRECTORY CommonJS resolver to packageURL, throwing a\nModule Not Found error for no resolution.
    5. \n
  5. \n

    If legacyMainURL does not end in \".js\" then,

    \n
      \n
    1. Throw an Unsupported File Extension error.
      2. \n
    \n
    6. \n
  6. Return legacyMainURL.
    7. \n
\n
\n

ESMFORMAT(_url, isMain)

\n
\n
    \n
  1. Assert: url corresponds to an existing file.
    2. \n
  2. Let pjson be the result of READ_PACKAGE_SCOPE(url).
    3. \n
  3. \n

    If url ends in \".mjs\", then

    \n
      \n
    1. Return \"module\".
      2. \n
    \n
    4. \n
  4. \n

    If url ends in \".cjs\", then

    \n
      \n
    1. Return \"commonjs\".
      2. \n
    \n
    5. \n
  5. \n

    If pjson?.type exists and is \"module\", then

    \n
      \n
    1. \n

      If isMain is true or url ends in \".js\", then

      \n
        \n
      1. Return \"module\".
        2. \n
      \n
      2. \n
    2. Throw an Unsupported File Extension error.
      3. \n
    \n
    6. \n
  6. \n

    Otherwise,

    \n
      \n
    1. \n

      If isMain is true or url ends in \".js\", \".json\" or\n\".node\", then

      \n
        \n
      1. Return \"commonjs\".
        2. \n
      \n
      2. \n
    2. Throw an Unsupported File Extension error.
      3. \n
    \n
    7. \n
\n
\n

READPACKAGE_SCOPE(_url)

\n
\n
    \n
  1. Let scopeURL be url.
    2. \n
  2. \n

    While scopeURL is not the file system root,

    \n
      \n
    1. Let pjson be the result of READ_PACKAGE_JSON(scopeURL).
      2. \n
    2. \n

      If pjson is not null, then

      \n
        \n
      1. Return pjson.
        2. \n
      \n
      3. \n
    3. Set scopeURL to the parent URL of scopeURL.
      4. \n
    \n
    3. \n
  3. Return null.
    4. \n
\n
\n

READPACKAGE_JSON(_packageURL)

\n
\n
    \n
  1. Let pjsonURL be the resolution of \"package.json\" within packageURL.
    2. \n
  2. \n

    If the file at pjsonURL does not exist, then

    \n
      \n
    1. Return null.
      2. \n
    \n
    3. \n
  3. \n

    If the file at packageURL does not parse as valid JSON, then

    \n
      \n
    1. Throw an Invalid Package Configuration error.
      2. \n
    \n
    4. \n
  4. Return the parsed JSON source of the file at pjsonURL.
    5. \n
\n
\n
", "type": "module", "displayName": "Resolver Algorithm" }, { "textRaw": "Customizing ESM specifier resolution algorithm", "name": "customizing_esm_specifier_resolution_algorithm", "desc": "

The current specifier resolution does not support all default behavior of\nthe CommonJS loader. One of the behavior differences is automatic resolution\nof file extensions and the ability to import directories that have an index\nfile.

\n

The --es-module-specifier-resolution=[mode] flag can be used to customize\nthe extension resolution algorithm. The default mode is explicit, which\nrequires the full path to a module be provided to the loader. To enable the\nautomatic extension resolution and importing from directories that include an\nindex file use the node mode.

\n
$ node --experimental-modules index.mjs\nsuccess!\n$ node --experimental-modules index #Failure!\nError: Cannot find module\n$ node --experimental-modules --es-module-specifier-resolution=node index\nsuccess!\n
", "type": "module", "displayName": "Customizing ESM specifier resolution algorithm" } ], "type": "misc", "displayName": "Resolution Algorithm" } ], "properties": [ { "textRaw": "`meta` {Object}", "type": "Object", "name": "meta", "desc": "

The import.meta metaproperty is an Object that contains the following\nproperty:

\n" } ] } ] }