title: Write a function that doubles up each item in an array
body: <p>This is in javascript.
  So far, I've got this:</p>
  
  <pre><code> var double = function (array) {
       var array = [];
       for(var i = 0; i&lt;array.length; i++) {
           var sum = array[i] + array[i];
       }
       return sum;
  };
  </code></pre>
  
  <p>...Basically, if I entered in this area:</p>
  
  <pre><code>var a = [1,2,3];
  </code></pre>
  
  <p>I would want the function to return:</p>
  
  <pre><code>[1,1,2,2,3,3]
  </code></pre>
  
  <p>...etc</p>