Javascript that calculates the difference between two times

Hi all..

I can't calculate the difference between two times fields.

For example: I have 3 dateTime fiels but in the Date Format I need only the time (hour)

How can I calculate the difference between 2 times?

time 1:  15:45:00

time2:   16:30:00

The result is: ....00:45:00

Thanks a Lot

María