delayedCallback(function(){ ... }, delay); // invoke the callback 'delay' ms after it is last called

delayedCallback.js

// returns a function that will invoke the callback 'delay' ms after it is last called
//   eg. invoke the callback 500ms after the last time a key is pressed
// based on http://stackoverflow.com/questions/2219924/idiomatic-jquery-delayed-event-only-after-a-short-pause-in-typing-e-g-timew
//   but fixes the following:
//   (a) returns a unique timer scope on every call
//   (b) propagates context and arguments from the last call to the returned closure
//   and adds .cancel() and .fire() for additional callback control
// then of course, you could use underscore's _.debounce
//   it doesn't have the .cancel and .fire, but you may not care :)
function delayedCallback(callback, delay) {
    return (function(callback, delay) {                          // (2) receives the values in scope
        var timer = 0;                                           // (3a) a scoped timer
        var context, args;                                       // (3b) scoped copies from the last invocation of the returned closure
        var cb = function() { callback.apply(context, args); }   // (3c) called with proper context + arguments
        var dcb = function() {                                   // (4) this closure is what gets returned from .delayedCallback
            context = this;
            args = arguments;
            window.clearTimeout(timer);
            timer = window.setTimeout(cb, delay);                // (5) only fires after this many ms of not re-invoking
        };
        dcb.cancel = function() { window.clearTimeout(timer); }; // (6a) you can cancel the delayed firing
        dcb.fire  = function() { this.cancel(); cb(); };         // (6b) or force it to fire immediately
        return dcb;
    })(callback, delay);                                         // (1) capture these values in scope
}