Allow trailing comma's (#2)

Author: hkrutzer

README.md

@@ -875,32 +875,99 @@ Forked from the excellent Airbnb JavaScript Style Guide, slightly modified to fi
     };
     ```
 
-  - Additional trailing comma: **Nope.** This can cause problems with IE6/7 and IE9 if it's in quirksmode. Also, in some implementations of ES3 would add length to an array if it had an additional trailing comma. This was clarified in ES5 ([source](http://es5.github.io/#D)):
+  - Additional trailing comma: **Yup.**
 
-  > Edition 5 clarifies the fact that a trailing comma at the end of an ArrayInitialiser does not add to the length of the array. This is not a semantic change from Edition 3 but some implementations may have previously misinterpreted this.
+  > Why? This leads to cleaner git diffs. Also, transpilers like Babel will remove the additional trailing comma in the transpiled code which means you don't have to worry about the [trailing comma problem](https://github.com/airbnb/javascript/blob/es5-deprecated/es5/README.md#commas) in legacy browsers.
+
+    ```diff
+    // bad - git diff without trailing comma
+    const hero = {
+         firstName: 'Florence',
+    -    lastName: 'Nightingale'
+    +    lastName: 'Nightingale',
+    +    inventorOf: ['coxcomb chart', 'modern nursing']
+    };
+
+    // good - git diff with trailing comma
+    const hero = {
+         firstName: 'Florence',
+         lastName: 'Nightingale',
+    +    inventorOf: ['coxcomb chart', 'modern nursing'],
+    };
+    ```
 
     ```javascript
     // bad
-    var hero = {
-      firstName: 'Kevin',
-      lastName: 'Flynn',
+    const hero = {
+      firstName: 'Dana',
+      lastName: 'Scully'
     };
 
-    var heroes = [
+    const heroes = [
       'Batman',
-      'Superman',
+      'Superman'
     ];
 
     // good
-    var hero = {
-      firstName: 'Kevin',
-      lastName: 'Flynn'
+    const hero = {
+      firstName: 'Dana',
+      lastName: 'Scully',
     };
 
-    var heroes = [
+    const heroes = [
       'Batman',
-      'Superman'
+      'Superman',
     ];
+
+    // bad
+    function createHero(
+      firstName,
+      lastName,
+      inventorOf
+    ) {
+      // does nothing
+    }
+
+    // good
+    function createHero(
+      firstName,
+      lastName,
+      inventorOf,
+    ) {
+      // does nothing
+    }
+
+    // good (note that a comma must not appear after a "rest" element)
+    function createHero(
+      firstName,
+      lastName,
+      inventorOf,
+      ...heroArgs
+    ) {
+      // does nothing
+    }
+
+    // bad
+    createHero(
+      firstName,
+      lastName,
+      inventorOf
+    );
+
+    // good
+    createHero(
+      firstName,
+      lastName,
+      inventorOf,
+    );
+
+    // good (note that a comma must not appear after a "rest" element)
+    createHero(
+      firstName,
+      lastName,
+      inventorOf,
+      ...heroArgs
+    )
     ```
 
     **[[⬆]](#TOC)**