module: deprecate module.parent

This feature does not work when a module is imported using ECMAScript modules specification, therefore it is deprecated. Fixes: nodejs/modules#469 PR-URL: #32217 Reviewed-By: Gus Caplan <[email protected]> Reviewed-By: Bradley Farias <[email protected]> Reviewed-By: Anna Henningsen <[email protected]> Reviewed-By: James M Snell <[email protected]> Reviewed-By: Matteo Collina <[email protected]> Reviewed-By: Tobias Nießen <[email protected]> Reviewed-By: Ruben Bridgewater <[email protected]>
nodejs · Aug 18, 2020 · 573ad3e · 573ad3e
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diff --git a/doc/api/deprecations.md b/doc/api/deprecations.md
@@ -2560,6 +2560,41 @@ written twice. This introduces a race condition between threads, and is a
 potential security vulnerability. There is no safe, cross-platform alternative
 API.
 
+<a id="DEP0144"></a>
+### DEP0144: `module.parent`
+<!-- YAML
+changes:
+  - version:
+    - REPLACEME
+    - v14.6.0
+    pr-url: https://github.com/nodejs/node/pull/32217
+    description: Documentation-only deprecation.
+-->
+
+Type: Documentation-only
+
+A CommonJS module can access the first module that required it using
+`module.parent`. This feature is deprecated because it does not work
+consistently in the presence of ECMAScript modules and because it gives an
+inaccurate representation of the CommonJS module graph.
+
+Some modules use it to check if they are the entry point of the current process.
+Instead, it is recommended to compare `require.main` and `module`:
+
+```js
+if (require.main === module) {
+  // Code section that will run only if current file is the entry point.
+}
+```
+
+When looking for the CommonJS modules that have required the current one,
+`require.cache` and `module.children` can be used:
+
+```js
+const moduleParents = Object.values(require.cache)
+  .filter((m) => m.children.includes(module));
+```
+
 [`--http-parser=legacy`]: cli.html#cli_http_parser_library
 [`--pending-deprecation`]: cli.html#cli_pending_deprecation
 [`--throw-deprecation`]: cli.html#cli_throw_deprecation

diff --git a/doc/api/modules.md b/doc/api/modules.md
@@ -894,11 +894,19 @@ loading.
 ### `module.parent`
 <!-- YAML
 added: v0.1.16
+deprecated:
+  - REPLACEME
+  - v14.6.0
 -->
 
-* {module}
+> Stability: 0 - Deprecated: Please use [`require.main`][] and
+> [`module.children`][] instead.
+
+* {module | null | undefined}
 
-The module that first required this one.
+The module that first required this one, or `null` if the current module is the
+entry point of the current process, or `undefined` if the module was loaded by
+something that is not a CommonJS module (E.G.: REPL or `import`).
 
 ### `module.path`
 <!-- YAML
@@ -1122,13 +1130,15 @@ consists of the following keys:
 [`createRequire()`]: #modules_module_createrequire_filename
 [`module` object]: #modules_the_module_object
 [`module.id`]: #modules_module_id
+[`module.children`]: #modules_module_children
 [`path.dirname()`]: path.html#path_path_dirname_path
 [ECMAScript Modules]: esm.html
 [an error]: errors.html#errors_err_require_esm
 [exports shortcut]: #modules_exports_shortcut
 [module resolution]: #modules_all_together
 [module wrapper]: #modules_the_module_wrapper
 [native addons]: addons.html
+[`require.main`]: #modules_require_main
 [source map include directives]: https://sourcemaps.info/spec.html#h.lmz475t4mvbx
 [`--enable-source-maps`]: cli.html#cli_enable_source_maps
 [`NODE_V8_COVERAGE=dir`]: cli.html#cli_node_v8_coverage_dir