Question

Just found this code-snippet in our application. I am wondering if the first line is superfluous — does one need to call clearTimeout on a variable if it is immediately overwritten? Or is there some condition I should be aware of?

function Countdown() {
    clearTimeout(sessionTimeoutHandle);
    sessionTimeoutHandle = setTimeout(function () { countdownHandler() }, MILLISECONDS);
}

My hunch is “Yes, you need to call clearTimeout” because I can’t think of why the clearTimeout method would exist if it was OK to just set the timeout variable to null.

I suppose the better question is:

var timeoutHandler = setTimeout(countdownHandler, MILLISECONDS);
timeoutHandler = setTimeout(countdownHandler, MILLISECONDS);

Do I now have two functions waiting to fire in approximately MILLISECONDS, or just one?

Answer 1

No, you only need to call it if you actually need to clear it.

If this is the only code using that variable, then there should be no need.

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FYI, it looks like you could shorten the code a bit…

function Countdown() {
    clearTimeout(sessionTimeoutHandle);
    sessionTimeoutHandle = setTimeout(countdownHandler, MILLISECONDS);
}

Nothing was gained with the anonymous function.