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Debouncing Javascript Methods
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05/15/2009, by John Hann
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Debouncing means to coalesce several temporally close signals into one signal. For example, your computer keyboard does this. Every time you hit a key, the contacts actually bounce a few times, causing several signals to be sent to the circuitry. The circuitry determines that the bouncing has ended when no bounces are detected within a certain period (the “detection period”). Since people can’t really type faster than roughly 10 keys per second, any signals happening within 100 msec of each other, for example, are likely part of the same key press. (In practice, you should at least halve this, so about 50 msec for our keyboard example. I have no idea what keyboards really use, by the way. This is just an illustration.)
Whenever I bring up the concept of debouncing, developers try to cast it as just a means of throttling. But that’s not true at all. Throttling is the reduction in rate of a repeating event. Throttling is good for reducing mousemove events to a lesser, manageable rate, for instance.
Debouncing is quite more precise. Debouncing ensures that exactly one signal is sent for an event that may be happening several times — or even several hundreds of times over an extended period. As long as the events are occurring fast enough to happen at least once in every detection period, the signal will not be sent!
Debouncing on the other hand could better detect when the user stopped leaning on the keyboard and had arrived at their destination. It’s certainly not perfect. The user still may overshoot their destination, hesitate, and back-track, causing enough delay for the debounce detection period to expire. However, our tests showed that debouncing did a much better job of reducing XHR requests than throttling.
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