title: Javascript array copying, concat vs slice, which one is better?
body: <p>there are two different ways to copy a array, using Array.concat or Array.slice, </p>
  
  <p>for example:</p>
  
  <pre><code>var a = [1, 2, 3],
  
      c1 = [].concat(a),
  
      c2 = a.slice(0);
  </code></pre>
  
  <p>which way is better?</p>