title: JavaScript push method changing values
body: <p>I am using Node shell to test this: BTW, I am new to Javascript</p>
  
  <pre><code>x = [1,2]
  y = [3,4]
  k = []
  for ( n in x.concat(y) ) { k.push(n); }
  </code></pre>
  
  <p>Now typing k prints the following:</p>
  
  <pre><code>[ '0', '1', '2', '3' ]
  </code></pre>