On Mar 25, 2013, at 1:57 AM, Claude Pache wrote:

> 
> Le 25 mars 2013 à 08:28, Axel Rauschmayer <axel at rauschma.de> a écrit :
> 
>> 2. Function expressions --> arrow functions
> 
> No, it depends. Roughly, I would replace function expressions by arrow functions when I want to use the 'this' binding of the enclosing scope (or don't use the 'this' binding), and the body is short. 
> 
> Random counter-example from my ES6 polyfill:
> 
>    if (typeof String.prototype.contains !== 'function') {
>        String.prototype.contains = function(x, p) {
>            return this.indexOf(x, p) !== -1
>        }
>        Object.defineProperty(String.prototype, 'contains', {enumerable: false})
>    }
> 
> I could not use an arrow expression (even if it existed in ES5) because I need a proper 'this' binding. In fact, I could hardly use anything else than a function expression.

You could use a concise method:


   if (typeof String.prototype.contains !== 'function') {
       String.prototype.contains = {contains(x, p) {return this.indexOf(x, p) !== -1}}.contains;
      }
    Object.defineProperty(String.prototype, 'contains', {enumerable: false})

or
   if (typeof String.prototype.contains !== 'function') {
       Object.assign(String.prototype, {contains(x, p) {return this.indexOf(x, p) !== -1}});  //or Object.mixin
       }
     Object.defineProperty(String.prototype, 'contains', {enumerable: false})
   }

Allen

On Mar 25, 2013, at 1:57 AM, Claude Pache wrote:

> 
> Le 25 mars 2013 ? 08:28, Axel Rauschmayer <axel at rauschma.de> a ?crit :
> 
>> 2. Function expressions --> arrow functions
> 
> No, it depends. Roughly, I would replace function expressions by arrow functions when I want to use the 'this' binding of the enclosing scope (or don't use the 'this' binding), and the body is short. 
> 
> Random counter-example from my ES6 polyfill:
> 
> ```js
> if (typeof String.prototype.contains !== 'function') {
>     String.prototype.contains = function(x, p) {
>         return this.indexOf(x, p) !== -1
>     }
>     Object.defineProperty(String.prototype, 'contains', {enumerable: false})
> }
> ```
> 
> I could not use an arrow expression (even if it existed in ES5) because I need a proper 'this' binding. In fact, I could hardly use anything else than a function expression.

You could use a concise method:


```js
if (typeof String.prototype.contains !== 'function') {
    String.prototype.contains = {contains(x, p) {return this.indexOf(x, p) !== -1}}.contains;
}
Object.defineProperty(String.prototype, 'contains', {enumerable: false})
```

or

```js
if (typeof String.prototype.contains !== 'function') {
    Object.assign(String.prototype, {contains(x, p) {return this.indexOf(x, p) !== -1}});  //or Object.mixin
}
Object.defineProperty(String.prototype, 'contains', {enumerable: false})
```

Allen