title: JavaScript for...in vs for
body: <p>Do you think there is a big difference in for...in and for loops? What kind of "for" do you prefer to use and why?</p>
  
  <p>Let's say we have an array of associative arrays:</p>
  
  <pre><code>var myArray = [{'key': 'value'}, {'key': 'value1'}];
  </code></pre>
  
  <p>So we can iterate:</p>
  
  <pre><code>for (var i = 0; i &lt; myArray.length; i++)
  </code></pre>
  
  <p>And:</p>
  
  <pre><code>for (var i in myArray)
  </code></pre>
  
  <p>I don't see a big difference. Are there any performance issues?</p>