How do I execute a Javascript function when a timer hits 0? For example, the timer should go from 5, 4, 3, 2, 1, 0 and t

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How do I execute a Javascript function when a timer hits 0? For
example, the timer should go from 5, 4, 3, 2, 1, 0 and then execute
a function at zero. The timer should also end when the timer hits
0. Please provide a code example of this working with your
answer.