Back to Zero

A stopwatch needs a way back to zero. In this exercise, it gets a Reset button, next to Start.

The task. A click on Reset puts the time back to 0.0 and stops the stopwatch, whether it's running or not, so that the other button says Start. While the time is 0.0, there's nothing to reset, and Reset is disabled.

A tip: Reset only has to change the state. You don't have to stop the interval yourself: when the running state changes to false, the effect's dependency changes, React calls the cleanup, and the cleanup stops the interval.