title: Momentjs and countdown timer
body: <p>I found the Momentjs library which is pretty cool, however I don't find the documentation to be very clear on how to achieve some simple tasks.
  I'm trying to build a countdown timer and I'm guessing I should use the duration object, but I don't quite understand how (maybe due to the fact that English isn't my first language). Anyways this is what I want:</p>
  
  <pre><code>var time = 7200;
  var duration = moment.duration('seconds',time);
  
  setInterval(function(){
    //show how many hours, minutes and secods are left
    $('.countdown').text(duration.format('h:mm:ss')); 
    //this doesn't work because there's no method format for the duration object.
  },1000);
  </code></pre>
  
  <p>So everysecond it should display:</p>
  
  <p>02:00:00</p>
  
  <p>01:59:59</p>
  
  <p>01:59:58</p>
  
  <p>01:59:57</p>
  
  <p>...</p>
  
  <p>00:00:00</p>
  
  <p>How would I achieve this result with the Momentjs library?
  Thanks!</p>