title: Extending built-in natives in ES6 with Babel
body: <p>I'm using Babel for extend my class with the built-in native Array</p>
  
  <pre><code>class NewArray extends Array {
    first() {
      return this[0];
    }
  }
  
  var a = new NewArray(1, 2, 3);
  console.log(a.length); // 3
  console.log(a); // [ 1, 2, 3 ]
  console.log(a.first()); // trigger error
  </code></pre>
  
  <p>In a.first(), I'm getting this error:</p>
  
  <pre><code>console.log(a.first());
                ^ 
  
  TypeError: a.first is not a function
  </code></pre>
  
  <p>Should I do something more to extend a built-in native?</p>
  
  <p>Thanks! </p>