Add prefer-date-now rule

docs/rules/prefer-date-now.md

@@ -0,0 +1,37 @@
+# Prefer `Date.now()` to get the number of milliseconds since the Unix Epoch
+
+[`Date.now()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/now) is shorter and nicer than [`new Date().getTime()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/getTime).
+
+This rule is fixable.
+
+## Fail
+
+```js
+const foo = new Date().getTime();
+```
+
+```js
+const foo = new Date().valueOf();
+```
+
+```js
+const foo = +new Date;
+```
+
+```js
+const foo = Number(new Date());
+```
+
+```js
+const foo = new Date() * 2;
+```
+
+## Pass
+
+```js
+const foo = Date.now();
+```
+
+```js
+const foo = Date.now() * 2;
+```

index.js

@@ -54,6 +54,7 @@ module.exports = {
 				'unicorn/prefer-add-event-listener': 'error',
 				'unicorn/prefer-array-find': 'error',
 				'unicorn/prefer-dataset': 'error',
+				'unicorn/prefer-date-now': 'error',
 				'unicorn/prefer-event-key': 'error',
 				// TODO: Enable this by default when targeting Node.js 12.
 				'unicorn/prefer-flat-map': 'off',

readme.md

@@ -69,6 +69,7 @@ Configure it in `package.json`.
 			"unicorn/prefer-add-event-listener": "error",
 			"unicorn/prefer-array-find": "error",
 			"unicorn/prefer-dataset": "error",
+			"unicorn/prefer-date-now": "error",
 			"unicorn/prefer-event-key": "error",
 			"unicorn/prefer-flat-map": "error",
 			"unicorn/prefer-includes": "error",
@@ -135,6 +136,7 @@ Configure it in `package.json`.
 - [prefer-add-event-listener](docs/rules/prefer-add-event-listener.md) - Prefer `.addEventListener()` and `.removeEventListener()` over `on`-functions. *(partly fixable)*
 - [prefer-array-find](docs/rules/prefer-array-find.md) - Prefer `.find(…)` over the first element from `.filter(…)`. *(partly fixable)*
 - [prefer-dataset](docs/rules/prefer-dataset.md) - Prefer using `.dataset` on DOM elements over `.setAttribute(…)`. *(fixable)*
+- [prefer-date-now](docs/rules/prefer-date-now.md) - Prefer `Date.now()` to get the number of milliseconds since the Unix Epoch. *(fixable)*
 - [prefer-event-key](docs/rules/prefer-event-key.md) - Prefer `KeyboardEvent#key` over `KeyboardEvent#keyCode`. *(partly fixable)*
 - [prefer-flat-map](docs/rules/prefer-flat-map.md) - Prefer `.flatMap(…)` over `.map(…).flat()`. *(fixable)*
 - [prefer-includes](docs/rules/prefer-includes.md) - Prefer `.includes()` over `.indexOf()` when checking for existence or non-existence. *(fixable)*

rules/prefer-date-now.js

@@ -0,0 +1,114 @@
+'use strict';
+const getDocumentationUrl = require('./utils/get-documentation-url');
+const methodSelector = require('./utils/method-selector');
+
+const MESSAGE_ID_DEFAULT = 'prefer-date';
+const MESSAGE_ID_METHOD = 'prefer-date-now-over-methods';
+const MESSAGE_ID_NUMBER = 'prefer-date-now-over-number-data-object';
+const messages = {
+	[MESSAGE_ID_DEFAULT]: 'Prefer `Date.now()` over `new Date()`.',
+	[MESSAGE_ID_METHOD]: 'Prefer `Date.now()` over `Date#{{method}}()`.',
+	[MESSAGE_ID_NUMBER]: 'Prefer `Date.now()` over `Number(new Date())`.'
+};
+
+const createNewDateSelector = path => {
+	const prefix = path ? `${path}.` : '';
+	return [
+		`[${prefix}type="NewExpression"]`,
+		`[${prefix}callee.type="Identifier"]`,
+		`[${prefix}callee.name="Date"]`,
+		`[${prefix}arguments.length=0]`
+	].join('');
+};
+
+const operatorsSelector = (...operators) => `:matches(${
+	operators.map(operator => `[operator="${operator}"]`).join(', ')
+})`;
+const newDateSelector = createNewDateSelector();
+const methodsSelector = [
+	methodSelector({
+		names: ['getTime', 'valueOf'],
+		length: 0
+	}),
+	createNewDateSelector('callee.object')
+].join('');
+const builtinObjectSelector = [
+	'CallExpression',
+	'[callee.type="Identifier"]',
+	':matches([callee.name="Number"], [callee.name="BigInt"])',
+	'[arguments.length=1]',
+	createNewDateSelector('arguments.0')
+].join('');
+// https://github.com/estree/estree/blob/master/es5.md#unaryoperator
+const unaryExpressionsSelector = [
+	'UnaryExpression',
+	operatorsSelector('+', '-'),
+	createNewDateSelector('argument')
+].join('');
+const assignmentExpressionSelector = [
+	'AssignmentExpression',
+	operatorsSelector('-=', '*=', '/=', '%=', '**='),
+	'>',
+	`${newDateSelector}.right`
+].join('');
+const binaryExpressionSelector = [
+	'BinaryExpression',
+	operatorsSelector('-', '*', '/', '%', '**'),
+	// Both `left` and `right` properties
+	'>',
+	newDateSelector
+].join('');
+
+const create = context => {
+	const report = (node, problem) => context.report({
+		node,
+		messageId: MESSAGE_ID_DEFAULT,
+		fix: fixer => fixer.replaceText(node, 'Date.now()'),
+		...problem
+	});
+
+	return {
+		[methodsSelector](node) {
+			const method = node.callee.property;
+			report(node, {
+				node: method,
+				messageId: MESSAGE_ID_METHOD,
+				data: {method: method.name}
+			});
+		},
+		[builtinObjectSelector](node) {
+			const {name} = node.callee;
+			if (name === 'Number') {
+				report(node, {
+					messageId: MESSAGE_ID_NUMBER
+				});
+			} else {
+				report(node.arguments[0]);
+			}
+		},
+		[unaryExpressionsSelector](node) {
+			report(node.operator === '-' ? node.argument : node);
+		},
+		[assignmentExpressionSelector](node) {
+			report(node);
+		},
+		[binaryExpressionSelector](node) {
+			report(node);
+		}
+	};
+};
+
+const schema = [];
+
+module.exports = {
+	create,
+	meta: {
+		type: 'suggestion',
+		docs: {
+			url: getDocumentationUrl(__filename)
+		},
+		fixable: 'code',
+		schema,
+		messages
+	}
+};

test/prefer-date-now.js

@@ -0,0 +1,104 @@
+import {test} from './utils/test';
+
+test({
+	valid: [
+		'const ts = Date.now()',
+
+		// Test `new Date()`
+		// Not `NewExpression`
+		'+Date()',
+		'+ Date',
+		// Not `Identifier`
+		'+ new window.Date()',
+		// Not `Date`
+		'+ new Moments()',
+		// More arguments
+		'+ new Date(0)',
+		'+ new Date(...[])',
+
+		// Test `new Date().getTime()` and `new Date().valueOf()`
+		// Not `CallExpression`
+		'new Date.getTime()',
+		// Not `MemberExpression`
+		'valueOf()',
+		// `computed`
+		'new Date()[getTime]()',
+		// Not `Identifier`
+		'new Date()["valueOf"]()',
+		// Not listed names
+		'new Date().notListed(0)',
+		// More arguments
+		'new Date().getTime(0)',
+		'new Date().valueOf(...[])',
+
+		// Test `Number(new Date())` and `BigInt(new Date())`
+		// Not `CallExpression`
+		'new Number(new Date())',
+		// Not `Identifier`
+		'window.BigInt(new Date())',
+		// Not listed names
+		'toNumber(new Date())',
+		// More/less arguments
+		'BigInt()',
+		'Number(new Date(), extraArgument)',
+		'BigInt([...new Date()])',
+
+		// Test `+ new Date()` / `- new Date()`
+		// Not `UnaryExpression`
+		'throw new Date()',
+		// Not `+/-`
+		'typeof new Date()',
+
+		// Test `AssignmentExpression`
+		// Not `AssignmentExpression`
+		'const foo = () => {return new Date()}',
+		// `operator` not listed
+		'foo += new Date()',
+
+		// Test `BinaryExpression`
+		// Not `BinaryExpression`
+		'function * foo() {yield new Date()}',
+		// `operator` not listed
+		'new Date() + new Date()',
+
+		// We are not checking these cases
+		'foo = new Date() | 0',
+		'foo &= new Date()',
+		'foo = new Date() >> 0'
+	],
+	invalid: []
+});
+
+test.visualize([
+	// `Date` methods
+	'const ts = new Date().getTime();',
+	'const ts = (new Date).getTime();',
+	'const ts = (new Date()).getTime();',
+	'const ts = new Date().valueOf();',
+	'const ts = (new Date).valueOf();',
+	'const ts = (new Date()).valueOf();',
+
+	// `Number()` and `BigInt()`
+	'const ts = /* 1 */ Number(/* 2 */ new /* 3 */ Date( /* 4 */ ) /* 5 */) /* 6 */',
+	'const tsBigInt = /* 1 */ BigInt(/* 2 */ new /* 3 */ Date( /* 4 */ ) /* 5 */) /* 6 */',
+
+	// `UnaryExpression`
+	'const ts = + /* 1 */ new Date;',
+	'const ts = - /* 1 */ new Date();',
+
+	// `BinaryExpression`
+	'const ts = new Date() - 0',
+	'const foo = bar - new Date',
+	'const foo = new Date() * bar',
+	'const ts = new Date() / 1',
+	'const ts = new Date() % Infinity',
+	'const ts = new Date() ** 1',
+	'const zero = (new Date(/* 1 */) /* 2 */) /* 3 */ - /* 4 */new Date',
+
+	// `AssignmentExpression`
+	'foo -= new Date()',
+	'foo *= new Date()',
+	'foo /= new Date',
+	'foo %= new Date()',
+	'foo **= new Date()'
+]);