JavaScript: Don’t spam your server, Debounce and Throttle

If you make server call-backs or update the browser GUI based on user interaction you can end up doing far more updates than necessary…

In fact on one occasion, during Illyriad-beta testing, we started tripping our server’s dynamic IP request rate throttling and banning our own IP address – D’oh!

Common situations where over responding to events are mousemove, keypress, resize and scroll; but there are a whole host of situations where this applies.

We update our pages dynamically via ajax, based on user clicks around the user interface. In this situation if the user makes several page navigation requests in quick succession – the only important one to be made is the last, as for all the previous ones the data will be thrown away. So why make the requests in the first place? It’s just unnecessary server load.

Equally, if a user is moving an mouse around a map and you are updating UI coordinates for every pixel change the mouse makes, it potentially a huge number of DOM updates far beyond the perception of a user; for no real benefit, but it will cause a degradation in performance.

Initially, we controlled the situation using complex setups of setTimeout clearTimeout and setInterval. However, as the various places we made use of this became more varied, with different sets of needs, the code became more and more complex and difficult to maintain.

Luckily, it was around this time we discovered Ben Alman’s jQuery plugins debounce and throttle; which are extremely powerful – yet simple to use of and cover a whole host of permutations.

Throttling

Using his  jQuery $.throttle, you can pass a delay and function to $.throttle to get a new function, that when called repetitively, executes the original function no more than once every delay milliseconds.

Throttling can be especially useful for rate limiting execution of handlers on events like resize and scroll. Check out the example for jQuery throttling.

Debouncing

Using his jQuery $.debounce, you can pass a delay and function to $.debounce to get a new function, that when called repetitively, executes the original function just once per “bunch” of calls, effectively coalescing multiple sequential calls into a single execution at either the beginning or end.

Debouncing can be especially useful for rate limiting execution of handlers on events that will trigger AJAX requests. Check out the example for jQuery debouncing.

In fact its well worth checking out all Ben Alman’s jQuery Projects as they are full of little wonders, that you soon are sure how you did without them!