title: new Date() set to 31 december 2014 says 1st december instead
body: <p>I am trying to convert a string to a Date object, and it works for all days except for December 31st where by object says December 1st instead of 31st. I have no idea why. Here is my <code>JavaScript</code> code:</p>
  
  <pre><code>var dt = new Date();
  dt.setDate("31");
  dt.setMonth("11");
  dt.setFullYear("2014");
  </code></pre>
  
  <p>but my variable value is:</p>
  
  <pre><code>Mon Dec 01 2014 11:48:08 GMT+0100 (Paris, Madrid)
  </code></pre>
  
  <p>If I do the same for any other date, my object returns to the appropriate value. Do you have any idea what I did wrong?</p>