New: no-class rule (fixes #2097)

conf/eslint.json

@@ -15,6 +15,7 @@
         "no-bitwise": 0,
         "no-caller": 2,
         "no-catch-shadow": 2,
+        "no-class": 0,
         "no-comma-dangle": 0,
         "no-cond-assign": 2,
         "no-console": 2,

docs/rules/README.md

@@ -178,6 +178,7 @@ These rules are purely matters of style and are quite subjective.
 
 These rules are only relevant to ES6 environments and are off by default.
 
+* [no-class](no-class.md) - avoid use of `class` (off by default)
 * [no-var](no-var.md) - require `let` or `const` instead of `var` (off by default)
 * [generator-star](generator-star.md) - **(deprecated)** enforce the position of the `*` in generator functions (off by default)
 * [generator-star-spacing](generator-star-spacing.md) - enforce the spacing around the `*` in generator functions (off by default)

docs/rules/no-class.md

@@ -0,0 +1,30 @@
+# Avoid use of `class` (no-class)
+
+ECMAScript 6 allows programmers to create `class` to "help" those coming from a OOP language, such as Java or C++, to create constructors, thus multiple instances of an object.
+In the JS community this is considered one of the bad parts (you can google it to read more about it).
+
+
+## Rule Details
+
+This rule aims to discourage the use of `class` and to encourage other approaches such as functional inheritance,
+prototypal inheritance or object composition.
+
+The following patterns are considered warnings:
+
+```js
+class Foo {
+  constructor() {
+    this.foo = 'bar';
+  }
+}
+```
+
+## When Not To Use It
+
+Existing ES6 JavaScript projects that are heavily using classical inheritance may not want to apply this rule if the cost of removing `class` is too costly.
+
+## Further Reading
+
+- https://www.youtube.com/watch?v=PSGEjv3Tqo0
+- https://medium.com/javascript-scene/the-two-pillars-of-javascript-ee6f3281e7f3
+- https://medium.com/@_ericelliott/how-to-fix-the-es6-class-keyword-2d42bb3f4caf

lib/rules/no-class.js

@@ -0,0 +1,27 @@
+/**
+ * @fileoverview Avoid using class inheritance, instead favor prototypes or object composition.
+ * @author Nicola Molinari
+ * @copyright 2015 Nicola Molinari. All rights reserved.
+ */
+"use strict";
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = function(context) {
+
+    //--------------------------------------------------------------------------
+    // Public
+    //--------------------------------------------------------------------------
+
+    return {
+
+        "ClassDeclaration": function(node) {
+            context.report(node, "Unexpected class declaration (with ecmaFeatures.classes enabled)" +
+              ", you should use other methods like prototypal inheritance or object composition.");
+        }
+
+    };
+
+};

tests/lib/rules/no-class.js

@@ -0,0 +1,40 @@
+/**
+ * @fileoverview Avoid using class inheritance, instead favor prototypes or object composition.
+ * @author Nicola Molinari
+ * @copyright 2015 Nicola Molinari. All rights reserved.
+ */
+"use strict";
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+var eslint = require("../../../lib/eslint"),
+    ESLintTester = require("eslint-tester");
+
+//------------------------------------------------------------------------------
+// Tests
+//------------------------------------------------------------------------------
+
+var eslintTester = new ESLintTester(eslint);
+eslintTester.addRuleTest("lib/rules/no-class", {
+
+    valid: [
+        {
+            code: "function foo() {}",
+            ecmaFeatures: { classes: true }
+        }
+    ],
+
+    invalid: [
+        {
+            code: "class Foo { constructor() { this.foo = 'bar'; } }",
+            ecmaFeatures: { classes: true },
+            errors: [{
+                message: "Unexpected class declaration (with ecmaFeatures.classes enabled)" +
+                  ", you should use other methods like prototypal inheritance or object composition.",
+                type: "ClassDeclaration"
+            }]
+        }
+    ]
+});