title: for ... in loop with string array outputs indices
body: <p>When I write some javascript such as this:</p>
  
  <pre><code>var words = ['word1', 'word2', 'word3']
  
  for (word in words) {
      console.log(word)
  }
  </code></pre>
  
  <p>The resulting output is the numeric indices of the respective word.  I did some searching on Google and I couldn't find the exact reason for this behavior.  I'm guessing that this is completely expected behavior but I would like to know the reason why.</p>
  
  <p>Thanks!</p>