Debouncer that keeps the last N calls active

debounceGroup.js

// Keep the last N calls active
// A regular debounce function would only keep a single function call
// on timeout at a time.
function debounceGroup(func, wait, groupSize) {
    var timeouts = []; // Use this array as a queue of method calls
    return function() {
        var context = this,
            args = Array.prototype.slice.call(arguments, 0);
        if (timeouts.length >= groupSize)
            clearTimeout(timeouts.shift());
        timeouts.push(setTimeout(function() {
            func.apply(context, args);
        }, wait));
    };
}

// If you need a varying group size:
function debounceGroupVarying(func, wait) {
    var timeouts = [];
    return function(groupSize) { // n is now passed as the first argument to the function 'func'
        var context = this,
            args = Array.prototype.slice.call(arguments, 1),
            removedTimeouts = timeouts.splice(0, timeouts.length - groupSize + 1);
        for (var i = 0; i < removedTimeouts.length; i++)
            clearTimeout(removedTimeouts[i]);
        timeouts.push(setTimeout(function() {
            func.apply(context, args);
        }, wait));
    };
}

usage.js

// Debounce a group of 4 method calls with a 200ms wait time
var debouncedLog = debounceGroup(function (someVar) {
    console.log(someVar);
}, 200, 4);

for (var i = 0; i < 10; i++)
    debouncedLog(i); // Prints only 6, 7, 8, 9

// ...and to have a debounced method with a varying group size:
// Note that the following is not a really good example since it
// essentially does the same as debounceGroup().
debouncedLog = debounceGroupVarying(function (someVar) {
    console.log(someVar);
}, 200);

for (var i = 0; i < 10; i++)
    debouncedLog(3, i); // Prints only 7, 8, 9