title: Why does parseInt yield NaN with Array#map?
body: <p>From the <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map" rel="noreferrer">Mozilla Developer Network</a>:</p>
  
  <pre><code>[1,4,9].map(Math.sqrt)
  </code></pre>
  
  <p>will yield:</p>
  
  <pre><code>[1,2,3]
  </code></pre>
  
  <p>Why then does this:</p>
  
  <pre><code>['1','2','3'].map(parseInt)
  </code></pre>
  
  <p>yield this:</p>
  
  <pre><code>[1, NaN, NaN]
  </code></pre>
  
  <p>I have tested in Firefox 3.0.1 and Chrome 0.3 and just as a disclaimer, I know this is not cross-browser functionality (no IE).</p>
  
  <p>I found out that the following will accomplish the desired effect. However, it still doesn’t explain the errant behavior of <code>parseInt</code>.</p>
  
  <pre><code>['1','2','3'].map(function(i){return +i;}) // returns [1,2,3]
  </code></pre>