title: for( in ) loop index is string instead of integer
body: <p>Consider following code:</p>
  
  <pre><code>var arr = [111, 222, 333];
  for(var i in arr) {
      if(i === 1) {
          // Never executed
      }
  }
  </code></pre>
  
  <p>It will fail, because <code>typeof i === 'string'</code>.</p>
  
  <p>Is there way around this? I could explicitly convert <code>i</code> to integer, but doing so seems to defeat the purpose using simpler <code>for in</code> instead of regular <code>for</code>-loop. </p>
  
  <p><strong>Edit:</strong></p>
  
  <p>I am aware of using <code>==</code> in comparison, but that is not an option.</p>