Merge pull request eslint#5920 from eslint/issue-5402

New: Add `no-useless-computed-key` rule

conf/eslint.json

@@ -114,6 +114,7 @@
         "no-unused-vars": "error",
         "no-use-before-define": "off",
         "no-useless-call": "off",
+        "no-useless-computed-key": "off",
         "no-useless-concat": "off",
         "no-useless-constructor": "off",
         "no-useless-escape": "off",

docs/rules/README.md

@@ -236,6 +236,7 @@ These rules relate to ES6, also known as ES2015:
 * [no-new-symbol](no-new-symbol.md): disallow `new` operators with the `Symbol` object (recommended)
 * [no-restricted-imports](no-restricted-imports.md): disallow specified modules when loaded by `import`
 * [no-this-before-super](no-this-before-super.md): disallow `this`/`super` before calling `super()` in constructors (recommended)
+* [no-useless-computed-key](no-useless-computed-key.md): disallow unnecessary computed property keys in object literals
 * [no-useless-constructor](no-useless-constructor.md): disallow unnecessary constructors
 * [no-var](no-var.md): require `let` or `const` instead of `var`
 * [object-shorthand](object-shorthand.md): require or disallow method and property shorthand syntax for object literals

docs/rules/no-useless-computed-key.md

@@ -0,0 +1,46 @@
+# Disallow unnecessary computed property keys on objects (no-useless-computed-key)
+
+It's unnecessary to use computed properties with literals such as:
+
+```js
+var foo = {["a"]: "b"};
+```
+
+The code can be rewritten as:
+
+```js
+var foo = {"a": "b"};
+```
+
+## Rule Details
+
+This rule disallows unnecessary usage of computed property keys.
+
+Examples of **incorrect** code for this rule:
+
+```js
+/*eslint no-useless-computed-key: "error"*/
+/*eslint-env es6*/
+
+var a = { ['0']: 0 };
+var a = { ['0+1,234']: 0 };
+var a = { [0]: 0 };
+var a = { ['x']: 0 };
+var a = { ['x']() {} };
+```
+
+Examples of **correct** code for this rule:
+
+```js
+/*eslint no-useless-computed-key: "error"*/
+
+var c = { 'a': 0 };
+var c = { 0: 0 };
+var a = { x() {} };
+var c = { a: 0 };
+var c = { '0+1,234': 0 };
+```
+
+## When Not To Use It
+
+If you don't want to be notified about unnecessary computed property keys, you can safely disable this rule.

docs/rules/object-shorthand.md

@@ -38,7 +38,7 @@ var foo = {
 ## Rule Details
 
 This rule enforces the use of the shorthand syntax. This applies
-to all methods (including generators) defined on object literals and any
+to all methods (including generators) defined in object literals and any
 properties defined where the key name matches name of the assigned variable.
 
 Each of the following properties would warn:

lib/rules/no-useless-computed-key.js

@@ -0,0 +1,37 @@
+/**
+ * @fileoverview Rule to disallow unnecessary computed property keys in object literals
+ * @author Burak Yigit Kaya
+ */
+"use strict";
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+var MESSAGE_UNNECESSARY_COMPUTED = "Unnecessarily computed property [{{property}}] found.";
+
+module.exports = {
+    meta: {
+        docs: {
+            description: "disallow unnecessary computed property keys in object literals",
+            category: "ECMAScript 6",
+            recommended: false
+        }
+    },
+    create: function(context) {
+        return {
+            "Property": function(node) {
+                if (!node.computed) {
+                    return;
+                }
+
+                var key = node.key,
+                    nodeType = typeof key.value;
+
+                if (key.type === "Literal" && (nodeType === "string" || nodeType === "number")) {
+                    context.report(node, MESSAGE_UNNECESSARY_COMPUTED, { property: context.getSource(key) });
+                }
+            }
+        };
+    }
+};

tests/lib/rules/no-useless-computed-key.js

@@ -0,0 +1,60 @@
+/**
+ * @fileoverview Tests for no-useless-computed-key rule.
+ * @author Burak Yigit Kaya
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+var rule = require("../../../lib/rules/no-useless-computed-key"),
+    RuleTester = require("../../../lib/testers/rule-tester");
+
+//------------------------------------------------------------------------------
+// Tests
+//------------------------------------------------------------------------------
+
+var ruleTester = new RuleTester();
+
+ruleTester.run("no-useless-computed-key", rule, {
+    valid: [
+        { code: "({ 'a': 0, b(){} })", env: { es6: true } },
+        { code: "({ [x]: 0 });", env: { es6: true } },
+        { code: "({ a: 0, [b](){} })", env: { es6: true } }
+    ],
+    invalid: [
+        {
+            code: "({ ['0']: 0 })",
+            env: {es6: true},
+            errors: [{
+                message: "Unnecessarily computed property ['0'] found.", type: "Property"
+            }]
+        }, {
+            code: "({ ['0+1,234']: 0 })",
+            env: {es6: true},
+            errors: [{
+                message: "Unnecessarily computed property ['0+1,234'] found.", type: "Property"
+            }]
+        }, {
+            code: "({ [0]: 0 })",
+            env: {es6: true},
+            errors: [{
+                message: "Unnecessarily computed property [0] found.", type: "Property"
+            }]
+        }, {
+            code: "({ ['x']: 0 })",
+            env: {es6: true},
+            errors: [{
+                message: "Unnecessarily computed property ['x'] found.", type: "Property"
+            }]
+        }, {
+            code: "({ ['x']() {} })",
+            env: {es6: true},
+            errors: [{
+                message: "Unnecessarily computed property ['x'] found.", type: "Property"
+            }]
+        }
+    ]
+});