eslint/lib/rules/no-eq-null.js

An AST-based pattern checker for JavaScript.

/**
 * @fileoverview Rule to flag comparisons to null without a type-checking
 * operator.
 * @author Ian Christian Myers
 */

"use strict";

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

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

		docs: {
			description:
				"Disallow `null` comparisons without type-checking operators",
			recommended: false,
			url: "https://eslint.org/docs/latest/rules/no-eq-null",
		},

		schema: [],

		messages: {
			unexpected: "Use '===' to compare with null.",
		},
	},

	create(context) {
		return {
			BinaryExpression(node) {
				const badOperator =
					node.operator === "==" || node.operator === "!=";

				if (
					(node.right.type === "Literal" &&
						node.right.raw === "null" &&
						badOperator) ||
					(node.left.type === "Literal" &&
						node.left.raw === "null" &&
						badOperator)
				) {
					context.report({ node, messageId: "unexpected" });
				}
			},
		};
	},
};