title: Javascript: setDate(DATE + day) not update month
body: <p>I created this function to increment a date (for a jQuery UI Datepicker):</p>
  
  <pre><code>function addDay(date) {
      var moreDay = new Date();
      var decomposed = date.split("-");
      var act = new Date(decomposed[2], decomposed[1], decomposed[0]);
      moreDay.setDate(act.getDate()+1);
      return moreDay;
  }
  </code></pre>
  
  <p>So, it scomposes the date (ex: 12-06-2013 (dd-mm-YYYY)) and put the values into a new Date, after that it addes a day. It works, but the month not change. Example, I changed the function into this:</p>
  
  <pre><code>function addDay() {
      var moreDay = new Date();
      var act = new Date(2013, 7, 3);
      moreDay.setDate(act.getDate()+1);
      alert(moreDay);
  }
  </code></pre>
  
  <p>And it returns Jun 4th 2013.. How it's possible?</p>