lib: add navigator.language & navigator.languages

Author: Uzlopak

doc/api/globals.md

@@ -637,6 +637,50 @@ logical processors available to the current Node.js instance.
 console.log(`This process is running on ${navigator.hardwareConcurrency} logical processors`);
 ```
 
+### `navigator.language`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+* {string}
+
+The `navigator.language` read-only property returns a string representing the
+preferred language of the Node.js instance.
+
+The value is representing the language version as defined in RFC <5646>.
+
+You can override the value of `navigator.language` by setting the
+`LC_ALL` environment variable.
+
+For example:
+```sh
+LC_ALL=fr-FR node -p "console.log(navigator.language)"
+```
+
+The fallback value on builds without ICU is `'en-US'`.
+
+```js
+console.log(`The preferred language of the Node.js instance has the tag '${navigator.language}'`);
+```
+
+### `navigator.languages`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+* {Array<string>}
+
+The `navigator.languages` read-only property returns an array of strings
+representing the preferred languages of the Node.js instance.
+By default it contains only the value of `navigator.language`.
+The fallback value on builds without ICU is `['en-US']`.
+
+```js
+console.log(`The preferred languages are '${navigator.language}'`);
+```
+
 ### `navigator.userAgent`
 
 <!-- YAML

lib/internal/navigator.js

@@ -2,9 +2,15 @@
 
 const {
   ObjectDefineProperties,
+  ObjectFreeze,
+  globalThis,
   Symbol,
 } = primordials;
 
+const {
+  Intl,
+} = globalThis;
+
 const {
   ERR_ILLEGAL_CONSTRUCTOR,
 } = require('internal/errors').codes;
@@ -24,6 +30,8 @@ class Navigator {
   // Private properties are used to avoid brand validations.
   #availableParallelism;
   #userAgent = `Node.js/${nodeVersion.slice(1, nodeVersion.indexOf('.'))}`;
+  #language = Intl?.Collator().resolvedOptions().locale || 'en-US';
+  #languages = ObjectFreeze([this.#language]);
 
   constructor() {
     if (arguments[0] === kInitialize) {
@@ -40,6 +48,20 @@ class Navigator {
     return this.#availableParallelism;
   }
 
+  /**
+   * @return {string}
+   */
+  get language() {
+    return this.#language;
+  }
+
+  /**
+   * @return {Array<string>}
+   */
+  get languages() {
+    return this.#languages;
+  }
+
   /**
    * @return {string}
    */
@@ -50,6 +72,8 @@ class Navigator {
 
 ObjectDefineProperties(Navigator.prototype, {
   hardwareConcurrency: kEnumerableProperty,
+  language: kEnumerableProperty,
+  languages: kEnumerableProperty,
   userAgent: kEnumerableProperty,
 });
 

test/parallel/test-navigator.js

@@ -1,7 +1,8 @@
 'use strict';
 
-require('../common');
+const common = require('../common');
 const assert = require('assert');
+const { execFile } = require('child_process');
 
 const is = {
   number: (value, key) => {
@@ -15,3 +16,44 @@ is.number(navigator.hardwareConcurrency, 'hardwareConcurrency');
 assert.ok(navigator.hardwareConcurrency > 0);
 assert.strictEqual(typeof navigator.userAgent, 'string');
 assert.match(navigator.userAgent, /^Node\.js\/\d+$/);
+
+assert.strictEqual(typeof navigator.language, 'string');
+assert.strictEqual(navigator.language, 'en-US');
+
+assert.ok(Array.isArray(navigator.languages));
+assert.strictEqual(navigator.languages.length, 1);
+assert.strictEqual(typeof navigator.languages[0], 'string');
+
+assert.throws(() => {
+  navigator.languages[0] = 'foo';
+}, new TypeError("Cannot assign to read only property '0' of object '[object Array]'"));
+assert.notStrictEqual(navigator.languages[0], 'foo');
+assert.strictEqual(navigator.languages[0], 'en-US');
+
+Object.defineProperty(navigator, 'language', { value: 'de-DE' });
+assert.strictEqual(navigator.language, 'de-DE');
+assert.strictEqual(navigator.languages.length, 1);
+assert.strictEqual(navigator.languages[0], 'en-US');
+
+
+if (common.hasIntl) {
+  {
+    const env = { ...process.env, LC_ALL: 'fr-FR' };
+    execFile(
+      process.execPath,
+      ['-p', 'process.exit(navigator.language === "fr-FR" ? 0 : 1)'],
+      { env },
+      common.mustSucceed()
+    );
+  }
+
+  {
+    const env = { ...process.env, LC_ALL: 'fr-FR' };
+    execFile(
+      process.execPath,
+      ['-p', 'process.exit(navigator.languages[0] === "fr-FR" ? 0 : 1)'],
+      { env },
+      common.mustSucceed()
+    );
+  }
+}