如何使用0:00:00格式递增数字？

I am trying to create a time tracker in the following format; 0:00:00. The first zero represents the hour, then minutes, then seconds. Currently, I have a working function that increments the number every second. I know there is a proper way to do this with getDate() and then modifying the hours, minutes and seconds using getHours(), getMinutes() and so on. I just can't seem to get it all to work together. I've attached a working jsFiddle to show how far I've gotten. I am trying to create a time tracker in the fol