limit.js Code Review

Question

I've written a quick little helper for event & call debounce/throttling. Since I'm at home and none of my regular code review friends are on-line I figured I'd turn to the great folks here! Would love any feedback you might have.

/**
 * debounce
 * @param {integer} milliseconds This param indicates the number of milliseconds
 *     to wait after the last call before calling the original function .
 * @return {function} This returns a function that when called will wait the
 *     indicated number of milliseconds after the last call before
 *     calling the original function.
 */
Function.prototype.debounce = function (milliseconds) {
    var baseFunction = this,
        timer = null,
        wait = milliseconds;

    return function () {
        var self = this,
            args = arguments;

        function complete() {
            baseFunction.apply(self, args);
            timer = null;
        }

        if (timer) {
            clearTimeout(timer);
        }

        timer = setTimeout(complete, wait);
    };
};

/**
* throttle
* @param {integer} milliseconds This param indicates the number of milliseconds
*     to wait between calls before calling the original function.
* @return {function} This returns a function that when called will wait the
*     indicated number of milliseconds between calls before
*     calling the original function.
*/
Function.prototype.throttle = function (milliseconds) {
    var baseFunction = this,
        lastEventTimestamp = null,
        limit = milliseconds;

    return function () {
        var self = this,
            args = arguments,
            now = Date.now();

        if (!lastEventTimestamp || now - lastEventTimestamp >= limit) {
            lastEventTimestamp = now;
            baseFunction.apply(self, args);
        }
    };
};

To help understand what the point of these helpers are I've prepared this demo: http://jsfiddle.net/zR5jV/1/

GitHub project can be found here: https://github.com/m-gagne/limit.js

Honestly, you'd probably be better off just using underscore.js, rather than reinventing the wheel (unless you're doing it for fun). At just around 4K minified, it's a very powerful library that includes more refined versions of both of these methods and is complimentary to almost every other JavaScript library. — blesh
– blesh, Commented Apr 26, 2012 at 19:46
Cool hadn't heard of underscore.js before, thanks. Yes this was more of a "do it for fun" / "try creating a project & associated website" project. It was also more to bring to light the issue of frequency of events that people might not know of. Rarely as a developer do we ever get to create something truly unique, but I've learned a lot and gotten some great feedback in producing this simple snippet of code :) — Marc Gagne
– Marc Gagne, Commented Apr 27, 2012 at 15:20

Bill Barry · Accepted Answer · 2012-04-24 20:27:58Z

The key differences between a throttled function and a debounced function are that the throttled function can return a value because it is called synchronously and the debounced version cannot because it is used asynchronously.

You have lost that on your throttle implementation. I would at least make the following change:

Function.prototype.throttle = function (milliseconds) {
    var baseFunction = this,
        lastEventTimestamp = null,
        limit = milliseconds,
        lastresult;

    return function () {
        var self = this,
            args = arguments,
            now = Date.now();

        if (!lastEventTimestamp || now - lastEventTimestamp >= limit) {
            lastEventTimestamp = now;
            lastresult = baseFunction.apply(self, args);
        }
        return lastresult;
    };
};

Good point, I've only used throttle in scenarios where I don't care about the return value. I'll integrate this into my library, thanks! — Marc Gagne
– Marc Gagne, Commented Apr 25, 2012 at 12:22

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