eslint-plugin-unicorn/rules/no-null.js

'use strict';
const getDocumentationUrl = require('./utils/get-documentation-url');
const methodSelector = require('./utils/method-selector');

const ERROR_MESSAGE_ID = 'error';
const SUGGESTION_REPLACE_MESSAGE_ID = 'replace';
const SUGGESTION_REMOVE_MESSAGE_ID = 'remove';

const objectCreateSelector = methodSelector({
	object: 'Object',
	name: 'create',
	length: 1
});

const selector = [
	`:not(${objectCreateSelector})`,
	'>',
	'Literal',
	'[raw="null"]'
].join('');

const isLooseEqual = node => node.type === 'BinaryExpression' && ['==', '!='].includes(node.operator);
const isStrictEqual = node => node.type === 'BinaryExpression' && ['===', '!=='].includes(node.operator);

const create = context => {
	const {checkStrictEquality} = {
		checkStrictEquality: false,
		...context.options[0]
	};

	return {
		[selector]: node => {
			const problem = {
				node,
				messageId: ERROR_MESSAGE_ID
			};

			/* istanbul ignore next */
			const {parent = {}} = node;

			if (!checkStrictEquality && isStrictEqual(parent)) {
				return;
			}

			const fix = fixer => fixer.replaceText(node, 'undefined');
			const replaceSuggestion = {
				messageId: SUGGESTION_REPLACE_MESSAGE_ID,
				fix
			};

			if (isLooseEqual(parent)) {
				problem.fix = fix;
			} else if (parent.type === 'ReturnStatement' && parent.argument === node) {
				problem.suggest = [
					{
						messageId: SUGGESTION_REMOVE_MESSAGE_ID,
						fix: fixer => fixer.remove(node)
					},
					replaceSuggestion
				];
			} else if (parent.type === 'VariableDeclarator' && parent.init === node && parent.parent.kind !== 'const') {
				problem.suggest = [
					{
						messageId: SUGGESTION_REMOVE_MESSAGE_ID,
						fix: fixer => fixer.removeRange([parent.id.range[1], node.range[1]])
					},
					replaceSuggestion
				];
			} else {
				problem.suggest = [
					replaceSuggestion
				];
			}

			context.report(problem);
		}
	};
};

const schema = [
	{
		type: 'object',
		properties: {
			checkStrictEquality: {
				type: 'boolean',
				default: false
			}
		},
		additionalProperties: false
	}
];

module.exports = {
	create,
	meta: {
		type: 'suggestion',
		docs: {
			url: getDocumentationUrl(__filename)
		},
		messages: {
			[ERROR_MESSAGE_ID]: 'Use `undefined` instead of `null`.',
			[SUGGESTION_REPLACE_MESSAGE_ID]: 'Replace `null` with `undefined`.',
			[SUGGESTION_REMOVE_MESSAGE_ID]: 'Remove `null`.'
		},
		schema,
		fixable: 'code'
	}
};