eslint/lib/rules/no-shadow-restricted-names.js

An AST-based pattern checker for JavaScript.

/**
 * @fileoverview Disallow shadowing of NaN, undefined, and Infinity (ES5 section 15.1.1)
 * @author Michael Ficarra
 */
"use strict";

/**
 * Determines if a variable safely shadows undefined.
 * This is the case when a variable named `undefined` is never assigned to a value (i.e. it always shares the same value
 * as the global).
 * @param {eslintScope.Variable} variable The variable to check
 * @returns {boolean} true if this variable safely shadows `undefined`
 */
function safelyShadowsUndefined(variable) {
	return (
		variable.name === "undefined" &&
		variable.references.every(ref => !ref.isWrite()) &&
		variable.defs.every(
			def =>
				def.node.type === "VariableDeclarator" &&
				def.node.init === null,
		)
	);
}

//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------

/** @type {import('../shared/types').Rule} */
module.exports = {
	meta: {
		type: "suggestion",

		docs: {
			description: "Disallow identifiers from shadowing restricted names",
			recommended: true,
			url: "https://eslint.org/docs/latest/rules/no-shadow-restricted-names",
		},

		schema: [],

		messages: {
			shadowingRestrictedName: "Shadowing of global property '{{name}}'.",
		},
	},

	create(context) {
		const RESTRICTED = new Set([
			"undefined",
			"NaN",
			"Infinity",
			"arguments",
			"eval",
		]);
		const sourceCode = context.sourceCode;

		// Track reported nodes to avoid duplicate reports. For example, on class declarations.
		const reportedNodes = new Set();

		return {
			"VariableDeclaration, :function, CatchClause, ImportDeclaration, ClassDeclaration, ClassExpression"(
				node,
			) {
				for (const variable of sourceCode.getDeclaredVariables(node)) {
					if (
						variable.defs.length > 0 &&
						RESTRICTED.has(variable.name) &&
						!safelyShadowsUndefined(variable)
					) {
						for (const def of variable.defs) {
							const nodeToReport = def.name;

							if (!reportedNodes.has(nodeToReport)) {
								reportedNodes.add(nodeToReport);
								context.report({
									node: nodeToReport,
									messageId: "shadowingRestrictedName",
									data: {
										name: variable.name,
									},
								});
							}
						}
					}
				}
			},
		};
	},
};