title: jQuery adding days to a date
body: <p>I am trying to add a number of days to a date selector input to get a start date and end date. I am getting an incorrect end date and cant see why.</p>
  
  <p>Example: Date selected 25-10-2011, days 1</p>
  
  <p>Result: date_start 2011-9-25, date_end 2012-5-7</p>
  
  <pre><code> function makeUpDates(){
        // concantenate values to date_start and date_end hidden inputs
        var dateString = document.getElementById('date').value,
        date = new Date(dateString);
        document.getElementById('date_start').value = date.getFullYear() + '-' + date.getMonth() + '-' + date.getDate();
  
        var numDays = document.getElementById('slider').value;
        date.setDate(date.getDate() + numDays);   
        var dateEnd = date.getFullYear() + '-' + date.getMonth() + '-' + date.getDate();
        document.getElementById('date_end').value = dateEnd;
   }
  </code></pre>