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lib: brand-check Navigator getters to throw ERR_INVALID_THIS #63601

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lib: brand-check Navigator getters to throw ERR_INVALID_THIS #63601

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a8d88e8
lib: brand-check Navigator getters to throw ERR_INVALID_THIS
May 27, 2026
57fda3b
fix: iterate Navigator.prototype instead of lists
May 28, 2026
a35e81b
fix: keep explicit brand check and rely on private field throw
May 31, 2026
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8 changes: 7 additions & 1 deletion lib/internal/navigator.js
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,7 @@ const {

const {
ERR_ILLEGAL_CONSTRUCTOR,
ERR_INVALID_THIS,
} = require('internal/errors').codes;

const {
Expand Down Expand Up @@ -79,7 +80,8 @@ function getNavigatorPlatform(arch, platform) {
}

class Navigator {
// Private properties are used to avoid brand validations.
// Private properties are used to avoid brand validations: reading a private
// field from a non-Navigator receiver throws a TypeError on its own.
#availableParallelism;
#locks;
#userAgent;
Expand Down Expand Up @@ -113,6 +115,10 @@ class Navigator {
* @returns {string}
*/
get language() {
// `language` does not read a private field, so brand-check explicitly
// to keep parity with the other getters when called on a non-Navigator
// receiver (e.g. `Navigator.prototype.language`).
if (!(#languages in this)) throw new ERR_INVALID_THIS('Navigator');
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@anonrig anonrig Jun 1, 2026

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We shouldn't do this. We explicitly avoided doing this because of performance in the past. We went through deprecation cycles multiple times because of this.

// The default locale might be changed dynamically, so always invoke the
// binding.
return getDefaultLocale() || 'en-US';
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16 changes: 16 additions & 0 deletions test/parallel/test-navigator.js
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Expand Up @@ -147,3 +147,19 @@ Object.defineProperty(navigator, 'language', { value: 'for-testing' });
assert.strictEqual(navigator.language, 'for-testing');
assert.strictEqual(navigator.languages.length, 1);
assert.strictEqual(navigator.languages[0] !== 'for-testing', true);

{
const { Navigator } = globalThis;
for (const name of Object.keys(Navigator.prototype)) {
assert.throws(
() => Navigator.prototype[name],
{ name: 'TypeError' },
`expected TypeError when reading ${name} on Navigator.prototype`,
);
assert.throws(
() => Reflect.get(Navigator.prototype, name, {}),
{ name: 'TypeError' },
`expected TypeError when reading ${name} on a plain object`,
);
}
}
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