no-shadow-restricted-names

Disallow identifiers from shadowing restricted names

ES2020 §18.1 Value Properties of the Global Object (globalThis, NaN, Infinity, undefined) as well as strict mode restricted identifiers eval and arguments are considered to be restricted names in JavaScript. Defining them to mean something else can have unintended consequences and confuse others reading the code. For example, there’s nothing preventing you from writing:

const undefined = "foo";
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Then any code used within the same scope would not get the global undefined, but rather the local version with a very different meaning.

Rule Details

Examples of incorrect code for this rule:

/*eslint no-shadow-restricted-names: "error"*/

function NaN(){}

!function(Infinity){};

const undefined = 5;

try {} catch(eval){}
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/*eslint no-shadow-restricted-names: "error"*/

import NaN from "foo";

import { undefined } from "bar";

class Infinity {}
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Examples of correct code for this rule:

/*eslint no-shadow-restricted-names: "error"*/

let Object;

function f(a, b){}

// Exception: `undefined` may be shadowed if the variable is never assigned a value.
let undefined;
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/*eslint no-shadow-restricted-names: "error"*/

import { undefined as undef } from "bar";
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Options

This rule has an object option:

• "reportGlobalThis": true (default false) reports declarations of globalThis.

reportGlobalThis

Examples of incorrect code for the { "reportGlobalThis": true } option:

/*eslint no-shadow-restricted-names: ["error", { "reportGlobalThis": true }]*/

const globalThis = "foo";
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/*eslint no-shadow-restricted-names: ["error", { "reportGlobalThis": true }]*/

function globalThis() {}
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/*eslint no-shadow-restricted-names: ["error", { "reportGlobalThis": true }]*/

import { globalThis } from "bar";
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/*eslint no-shadow-restricted-names: ["error", { "reportGlobalThis": true }]*/

class globalThis {}
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Examples of correct code for the { "reportGlobalThis": true } option:

/*eslint no-shadow-restricted-names: ["error", { "reportGlobalThis": true }]*/

const foo = globalThis;

function bar() {
    return globalThis;
}

import { globalThis as baz } from "foo";
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Related Rules

• no-shadow

Version

This rule was introduced in ESLint v0.1.4.

Further Reading

ECMAScript® 2020 Language Specification
262.ecma-international.org

ECMAScript® 2020 Language Specification
262.ecma-international.org

Resources

• Rule source
• Tests source