eslint-plugin-unicorn/rules/no-new-array.js

More than 100 powerful ESLint rules

import {isParenthesized, getStaticValue} from '@eslint-community/eslint-utils';
import needsSemicolon from './utils/needs-semicolon.js';
import isNumber from './utils/is-number.js';
import {isNewExpression} from './ast/index.js';

const MESSAGE_ID_ERROR = 'error';
const MESSAGE_ID_LENGTH = 'array-length';
const MESSAGE_ID_ONLY_ELEMENT = 'only-element';
const MESSAGE_ID_SPREAD = 'spread';
const messages = {
	[MESSAGE_ID_ERROR]: '`new Array()` is unclear in intent; use either `[x]` or `Array.from({length: x})`',
	[MESSAGE_ID_LENGTH]: 'The argument is the length of array.',
	[MESSAGE_ID_ONLY_ELEMENT]: 'The argument is the only element of array.',
	[MESSAGE_ID_SPREAD]: 'Spread the argument.',
};

function getProblem(context, node) {
	if (
		!isNewExpression(node, {
			name: 'Array',
			argumentsLength: 1,
			allowSpreadElement: true,
		})
	) {
		return;
	}

	const problem = {
		node,
		messageId: MESSAGE_ID_ERROR,
	};

	const [argumentNode] = node.arguments;

	const {sourceCode} = context;
	let text = sourceCode.getText(argumentNode);
	if (isParenthesized(argumentNode, sourceCode)) {
		text = `(${text})`;
	}

	const maybeSemiColon = needsSemicolon(sourceCode.getTokenBefore(node), sourceCode, '[')
		? ';'
		: '';

	// We are not sure how many `arguments` passed
	if (argumentNode.type === 'SpreadElement') {
		problem.suggest = [
			{
				messageId: MESSAGE_ID_SPREAD,
				fix: fixer => fixer.replaceText(node, `${maybeSemiColon}[${text}]`),
			},
		];
		return problem;
	}

	const fromLengthText = `Array.from(${text === 'length' ? '{length}' : `{length: ${text}}`})`;
	const scope = sourceCode.getScope(node);
	if (isNumber(argumentNode, scope)) {
		problem.fix = fixer => fixer.replaceText(node, fromLengthText);
		return problem;
	}

	const onlyElementText = `${maybeSemiColon}[${text}]`;
	const result = getStaticValue(argumentNode, scope);
	if (result !== null && typeof result.value !== 'number') {
		problem.fix = fixer => fixer.replaceText(node, onlyElementText);
		return problem;
	}

	// We don't know the argument is number or not
	problem.suggest = [
		{
			messageId: MESSAGE_ID_LENGTH,
			fix: fixer => fixer.replaceText(node, fromLengthText),
		},
		{
			messageId: MESSAGE_ID_ONLY_ELEMENT,
			fix: fixer => fixer.replaceText(node, onlyElementText),
		},
	];
	return problem;
}

/** @param {import('eslint').Rule.RuleContext} context */
const create = context => ({
	NewExpression(node) {
		return getProblem(context, node);
	},
});

/** @type {import('eslint').Rule.RuleModule} */
const config = {
	create,
	meta: {
		type: 'suggestion',
		docs: {
			description: 'Disallow `new Array()`.',
			recommended: true,
		},
		fixable: 'code',
		hasSuggestions: true,
		messages,
	},
};

export default config;