title: Why does changing one array alters the other?
body: <p>Consider this tiny bit of javascript code:</p>
  
  <pre><code>var a = [1, 2, 3],
      b = a;
  
  b[1] = 3;
  
  a; // a === [1, 3, 3] wtf!?
  </code></pre>
  
  <p>Why does "a" change when I update "b[1]"? I've tested it in Firefox and Chrome. This doesn't happen to a simple number for example. Is this the expected behaviour?</p>
  
  <pre><code>var a = 1,
      b = a;
  
  b = 3;
  
  a; // a === 1 phew!
  </code></pre>