Check this out: 

https://github.com/tafsiri/gaia/blob/b62f522617e580d83d3e44d3e69f5b4f3ef95185/apps/clock/js/stopwatch_panel.js#L168-L171

I don't know why that's being made into a string, but it shouldn't be. While you're in this file, Please remove the `+ '';`