Dynamic date and time with moment.js and setInterval

I'm trying to find out how I can display dynamic date and time using moment.js.

Apparently I can't figure out to use setInterval properly.

If possible I'd prefer not to use jQuery as moment.js dosn't need it.

Here's what I have so far: http://jsfiddle.net/37fLF/2/.

$(document).ready(function () {
    var datetime = $('#datetime'),
        date = moment(new Date()),
        update = function(){
            datetime.html(date.format('dddd, MMMM Do YYYY, h:mm:ss a'));
        };
    update();
    setInterval(update, 1000);
});​