Add prefer-trim-start-end rule (#440)

docs/rules/prefer-trim-start-end.md

@@ -0,0 +1,19 @@
+# Prefer `String#trimStart()` / `String#trimEnd()` over `String#trimLeft()` / `String#trimRight()`
+
+[`String#trimLeft()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/trimLeft) and [`String#trimRight()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/trimRight) are aliases of [`String#trimStart()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/trimStart) and [`String#trimEnd()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/trimEnd)
+
+This rule is fixable.
+
+## Fail
+
+```js
+const foo = bar.trimStart();
+const foo = bar.trimEnd();
+```
+
+## Pass
+
+```js
+const foo = bar.trimLeft();
+const foo = bar.trimRight();
+```

index.js

@@ -57,6 +57,7 @@ module.exports = {
 				'unicorn/prefer-starts-ends-with': 'error',
 				'unicorn/prefer-string-slice': 'error',
 				'unicorn/prefer-text-content': 'error',
+				'unicorn/prefer-trim-start-end': 'error',
 				'unicorn/prefer-type-error': 'error',
 				'unicorn/prevent-abbreviations': 'error',
 				'unicorn/regex-shorthand': 'error',

readme.md

@@ -75,6 +75,7 @@ Configure it in `package.json`.
 			"unicorn/prefer-starts-ends-with": "error",
 			"unicorn/prefer-string-slice": "error",
 			"unicorn/prefer-text-content": "error",
+			"unicorn/prefer-trim-start-end": "error",
 			"unicorn/prefer-type-error": "error",
 			"unicorn/prevent-abbreviations": "error",
 			"unicorn/regex-shorthand": "error",
@@ -126,6 +127,7 @@ Configure it in `package.json`.
 - [prefer-starts-ends-with](docs/rules/prefer-starts-ends-with.md) - Prefer `String#startsWith()` & `String#endsWith()` over more complex alternatives.
 - [prefer-string-slice](docs/rules/prefer-string-slice.md) - Prefer `String#slice()` over `String#substr()` and `String#substring()`. *(partly fixable)*
 - [prefer-text-content](docs/rules/prefer-text-content.md) - Prefer `.textContent` over `.innerText`. *(fixable)*
+- [prefer-trim-start-end](docs/rules/prefer-trim-start-end.md) - Prefer `String#trimStart()` / `String#trimEnd()` over `String#trimLeft()` / `String#trimRight()`. *(fixable)*
 - [prefer-type-error](docs/rules/prefer-type-error.md) - Enforce throwing `TypeError` in type checking conditions. *(fixable)*
 - [prevent-abbreviations](docs/rules/prevent-abbreviations.md) - Prevent abbreviations. *(partly fixable)*
 - [regex-shorthand](docs/rules/regex-shorthand.md) - Enforce the use of regex shorthands to improve readability. *(fixable)*

rules/prefer-trim-start-end.js

@@ -0,0 +1,55 @@
+'use strict';
+const getDocumentationUrl = require('./utils/get-documentation-url');
+
+const methods = new Map([
+	['trimLeft', 'trimStart'],
+	['trimRight', 'trimEnd']
+]);
+
+const messages = {};
+
+for (const [method, replacement] of methods.entries()) {
+	messages[method] = `Prefer \`String#${method}()\` over \`String#${replacement}()\`.`;
+}
+
+const create = context => {
+	return {
+		CallExpression(node) {
+			const {callee, arguments: arguments_} = node;
+
+			if (
+				callee.type !== 'MemberExpression' ||
+				callee.property.type !== 'Identifier' ||
+				arguments_.length !== 0
+			) {
+				return;
+			}
+
+			const method = callee.property.name;
+
+			if (!methods.has(method)) {
+				return;
+			}
+
+			const replacement = methods.get(method);
+
+			context.report({
+				node,
+				messageId: method,
+				fix: fixer => fixer.replaceText(callee.property, replacement)
+			});
+		}
+	};
+};
+
+module.exports = {
+	create,
+	meta: {
+		type: 'suggestion',
+		docs: {
+			url: getDocumentationUrl(__filename)
+		},
+		fixable: 'code',
+		messages
+	}
+};

test/prefer-trim-start-end.js

@@ -0,0 +1,51 @@
+import test from 'ava';
+import avaRuleTester from 'eslint-ava-rule-tester';
+import rule from '../rules/prefer-trim-start-end';
+
+const ruleTester = avaRuleTester(test, {
+	env: {
+		es6: true
+	}
+});
+
+const errorTrimLeft = {
+	ruleId: 'prefer-trim-start-end',
+	messageId: 'trimLeft'
+};
+
+const errorTrimRight = {
+	ruleId: 'prefer-trim-start-end',
+	messageId: 'trimRight'
+};
+
+ruleTester.run('prefer-flat-map', rule, {
+	valid: [
+		'foo.trimStart()',
+		'foo.trimEnd()',
+		// Extra arguments
+		'foo.trimLeft(1)',
+		// New
+		'new foo.trimLeft()',
+		// Function call
+		'trimLeft()',
+		// Not call
+		'foo.trimLeft'
+	],
+	invalid: [
+		{
+			code: 'foo.trimLeft()',
+			output: 'foo.trimStart()',
+			errors: [errorTrimLeft]
+		},
+		{
+			code: 'foo.trimRight()',
+			output: 'foo.trimEnd()',
+			errors: [errorTrimRight]
+		},
+		{
+			code: '"foo".trimLeft()',
+			output: '"foo".trimStart()',
+			errors: [errorTrimLeft]
+		}
+	]
+});