javascript - When using setTimeout do you have to clearTimeout? - Stack Overflow

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Someone told me that when you use setTimeout you must clear it with clearTimeout. I can understand before the timeout runs out, but why after? Or is it untrue?

Someone told me that when you use setTimeout you must clear it with clearTimeout. I can understand before the timeout runs out, but why after? Or is it untrue?

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Share Improve this question Follow asked Sep 12, 2011 at 17:23 NebulaFoxNebulaFox 8,28199 gold badges5151 silver badges6767 bronze badges

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Sorted by: Reset to default 148

It's not true - there's no harm in clearing a timeout after it has finished, but it's not necessary.

Per the specification:

If handle does not identify an entry in the list of active timers of the WindowOrWorkerGlobalScope object on which [clearTimeout] was invoked, the method does nothing.

In other words, it's a no-op; nothing happens, and no error will be thrown.

You don't actually need to use clearTimeout, you only use it if you wish to cancel the timeout you already set before it happens.

It's usually more practical to use clearInterval with setInterval because setInterval usually runs indefinitely.

clearTimeout is only necessary for cancelling a timeout. After the timeout fires, it can safely be left alone. clearInterval is much more typically necessary to prevent it from continuing indefinitely.

No, setTimeout stops running after 1 call. In order to stop setInterval however, you must use clearInterval. If you create an endless loop of setTimeout then clearTimeout could be used.

No reason to clear it after it's completed. Your friend might have been confused with setInterval.

It is always best practice to cleartimeout after using setTimeout. let's take a scenario you are using setTimeout on /abc page. and you set a time of 10s. and now you move to /something page before the timeout is completed(less than 10s). but setTimeout is still running so now you are on /something page and timeout ends the time and the callback function will run on /something page in the callback function, you might be using a window object which may affect your /something page and result in an error or unexpected result.

conclusion- always use cleartimeout to remove unexpected errors.

Please add your thoughts if I am wrong

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