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Oct 31, 2025
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doc: correct module loading descriptions #60346

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b79756e
doc: correct module loading descriptions
joyeecheung Oct 21, 2025
b10e129
fixup! doc: correct module loading descriptions
joyeecheung Oct 31, 2025
295771c
fixup! fixup! doc: correct module loading descriptions
joyeecheung Oct 31, 2025
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28 changes: 9 additions & 19 deletions doc/api/cli.md
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Expand Up @@ -25,30 +25,22 @@ For more info about `node inspect`, see the [debugger][] documentation.

The program entry point is a specifier-like string. If the string is not an
absolute path, it's resolved as a relative path from the current working
directory. That path is then resolved by [CommonJS][] module loader. If no
corresponding file is found, an error is thrown.
directory. That entry point string is then resolved as if it's been requested
by `require()` from the current working directory. If no corresponding file
is found, an error is thrown.

If a file is found, its path will be passed to the
[ES module loader][Modules loaders] under any of the following conditions:
By default, the resolved path is also loaded as if it's been requested by `require()`,
unless one of the conditions below apply—then it's loaded as if it's been requested
by `import()`:

* The program was started with a command-line flag that forces the entry
point to be loaded with ECMAScript module loader, such as `--import`.
* The file has an `.mjs` or `.wasm` extension.
* The file has an `.mjs`, `.mts` or `.wasm` extension.
* The file does not have a `.cjs` extension, and the nearest parent
`package.json` file contains a top-level [`"type"`][] field with a value of
`"module"`.

Otherwise, the file is loaded using the CommonJS module loader. See
[Modules loaders][] for more details.

### ECMAScript modules loader entry point caveat

When loading, the [ES module loader][Modules loaders] loads the program
entry point, the `node` command will accept as input only files with `.js`,
`.mjs`, or `.cjs` extensions. With the following flags, additional file
extensions are enabled:

* [`--experimental-addon-modules`][] for files with `.node` extension.
See [module resolution and loading][] for more details.

## Options

Expand Down Expand Up @@ -4073,7 +4065,6 @@ node --stack-trace-limit=12 -p -e "Error.stackTraceLimit" # prints 12
[#42511]: https://github.com/nodejs/node/issues/42511
[Chrome DevTools Protocol]: https://chromedevtools.github.io/devtools-protocol/
[Chromium's policy for locally trusted certificates]: https://chromium.googlesource.com/chromium/src/+/main/net/data/ssl/chrome_root_store/faq.md#does-the-chrome-certificate-verifier-consider-local-trust-decisions
[CommonJS]: modules.md
[CommonJS module]: modules.md
[DEP0025 warning]: deprecations.md#dep0025-requirenodesys
[ECMAScript module]: esm.md#modules-ecmascript-modules
Expand All @@ -4083,7 +4074,7 @@ node --stack-trace-limit=12 -p -e "Error.stackTraceLimit" # prints 12
[Loading ECMAScript modules using `require()`]: modules.md#loading-ecmascript-modules-using-require
[Module customization hooks]: module.md#customization-hooks
[Module customization hooks: enabling]: module.md#enabling
[Modules loaders]: packages.md#modules-loaders
[Module resolution and loading]: packages.md#module-resolution-and-loading
[Navigator API]: globals.md#navigator
[Node.js issue tracker]: https://github.com/nodejs/node/issues
[OSSL_PROVIDER-legacy]: https://www.openssl.org/docs/man3.0/man7/OSSL_PROVIDER-legacy.html
Expand All @@ -4109,7 +4100,6 @@ node --stack-trace-limit=12 -p -e "Error.stackTraceLimit" # prints 12
[`--disable-sigusr1`]: #--disable-sigusr1
[`--env-file-if-exists`]: #--env-file-if-existsfile
[`--env-file`]: #--env-filefile
[`--experimental-addon-modules`]: #--experimental-addon-modules
[`--experimental-sea-config`]: single-executable-applications.md#generating-single-executable-preparation-blobs
[`--heap-prof-dir`]: #--heap-prof-dir
[`--import`]: #--importmodule
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96 changes: 55 additions & 41 deletions doc/api/packages.md
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Expand Up @@ -142,46 +142,56 @@ CommonJS. This includes the following:
* Lexical redeclarations of the CommonJS wrapper variables (`require`, `module`,
`exports`, `__dirname`, `__filename`).

### Modules loaders

Node.js has two systems for resolving a specifier and loading modules.

There is the CommonJS module loader:

* It is fully synchronous.
* It is responsible for handling `require()` calls.
* It is monkey patchable.
* It supports [folders as modules][].
* When resolving a specifier, if no exact match is found, it will try to add
extensions (`.js`, `.json`, and finally `.node`) and then attempt to resolve
[folders as modules][].
* It treats `.json` as JSON text files.
* `.node` files are interpreted as compiled addon modules loaded with
`process.dlopen()`.
* It treats all files that lack `.json` or `.node` extensions as JavaScript
text files.
* It can only be used to [load ECMAScript modules from CommonJS modules][] if
the module graph is synchronous (that contains no top-level `await`).
When used to load a JavaScript text file that is not an ECMAScript module,
the file will be loaded as a CommonJS module.

There is the ECMAScript module loader:

* It is asynchronous, unless it's being used to load modules for `require()`.
* It is responsible for handling `import` statements and `import()` expressions.
* It is not monkey patchable, can be customized using [loader hooks][].
* It does not support folders as modules, directory indexes (e.g.
`'./startup/index.js'`) must be fully specified.
* It does no extension searching. A file extension must be provided
when the specifier is a relative or absolute file URL.
* It can load JSON modules, but an import type attribute is required.
* It accepts only `.js`, `.mjs`, and `.cjs` extensions for JavaScript text
files.
* It can be used to load JavaScript CommonJS modules. Such modules
are passed through the `cjs-module-lexer` to try to identify named exports,
which are available if they can be determined through static analysis.
Imported CommonJS modules have their URLs converted to absolute
paths and are then loaded via the CommonJS module loader.
### Module resolution and loading

Node.js has two types of module resolution and loading, chosen based on how the module is requested.

When a module is requested via `require()` (available by default in CommonJS modules,
and can be dynamically generated using `createRequire()` in both CommonJS and ES Modules):

* Resolution:
* The resolution initiated by `require()` supports [folders as modules][].
* When resolving a specifier, if no exact match is found, `require()` will try to add
extensions (`.js`, `.json`, and finally `.node`) and then attempt to resolve
[folders as modules][].
* It does not support URLs as specifiers by default.
* Loading:
* `.json` files are treated as JSON text files.
* `.node` files are interpreted as compiled addon modules loaded with `process.dlopen()`.
* `.ts`, `.mts` and `.cts` files are treated as [TypeScript][] text files.
* Files with any other extension, or without extensions, are treated as JavaScript
text files.
* `require()` can only be used to [load ECMAScript modules from CommonJS modules][] if
the [ECMAScript module][ES Module] _and its dependencies_ are synchronous
(i.e. they do not contain top-level `await`).

When a module is requested via static `import` statements (only available in ES Modules)
or `import()` expressions (available in both CommonJS and ES Modules):

* Resolution:
* The resolution of `import`/`import()` does not support folders as modules,
directory indexes (e.g. `'./startup/index.js'`) must be fully specified.
* It does not perform extension searching. A file extension must be provided
when the specifier is a relative or absolute file URL.
* It supports `file://` and `data:` URLs as specifiers by default.
* Loading:
* `.json` files are treated as JSON text files. When importing JSON modules,
an import type attribute is required (e.g.
`import json from './data.json' with { type: 'json' }`).
* `.node` files are interpreted as compiled addon modules loaded with
`process.dlopen()`, if [`--experimental-addon-modules`][] is enabled.
* `.ts`, `.mts` and `.cts` files are treated as [TypeScript][] text files.
* It accepts only `.js`, `.mjs`, and `.cjs` extensions for JavaScript text
files.
* `.wasm` files are treated as [WebAssembly modules][].
* Any other file extensions will result in a [`ERR_UNKNOWN_FILE_EXTENSION`][] error.
Additional file extensions can be facilitated via [customization hooks][].
* `import`/`import()` can be used to load JavaScript [CommonJS modules][commonjs].
Such modules are passed through the `cjs-module-lexer` to try to identify named
exports, which are available if they can be determined through static analysis.

Regardless of how a module is requested, the resolution and loading process can be customized
using [customization hooks][].

### `package.json` and file extensions

Expand Down Expand Up @@ -1151,21 +1161,25 @@ This field defines [subpath imports][] for the current package.
[Node.js documentation for this section]: https://github.com/nodejs/node/blob/HEAD/doc/api/packages.md#conditions-definitions
[Runtime Keys]: https://runtime-keys.proposal.wintercg.org/
[Syntax detection]: #syntax-detection
[TypeScript]: typescript.md
[WebAssembly modules]: esm.md#wasm-modules
[WinterCG]: https://wintercg.org/
[`"exports"`]: #exports
[`"imports"`]: #imports
[`"main"`]: #main
[`"name"`]: #name
[`"type"`]: #type
[`--conditions` / `-C` flag]: #resolving-user-conditions
[`--experimental-addon-modules`]: cli.md#--experimental-addon-modules
[`--no-addons` flag]: cli.md#--no-addons
[`ERR_PACKAGE_PATH_NOT_EXPORTED`]: errors.md#err_package_path_not_exported
[`ERR_UNKNOWN_FILE_EXTENSION`]: errors.md#err_unknown_file_extension
[`package.json`]: #nodejs-packagejson-field-definitions
[customization hooks]: module.md#customization-hooks
[entry points]: #package-entry-points
[folders as modules]: modules.md#folders-as-modules
[import maps]: https://github.com/WICG/import-maps
[load ECMAScript modules from CommonJS modules]: modules.md#loading-ecmascript-modules-using-require
[loader hooks]: esm.md#loaders
[packages folder mapping]: https://github.com/WICG/import-maps#packages-via-trailing-slashes
[self-reference]: #self-referencing-a-package-using-its-name
[subpath exports]: #subpath-exports
Expand Down
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