makeFunctionSerial.js

var Q = require("q");
var Queue = require("q/queue").Queue;

function throttle(max, wrapped) {
    var queue = Queue();
    var pending = 0;

    function loop() {
        return Q.when(queue.get(), function (next) {
            var done = Q.defer();
            function wrap(callback) {
                return function () {
                    done.resolve(callback.apply(this, arguments));
                }
            }
            wrapped.apply(next["this"], [wrap].concat(next["args"]));
            return Q.when(done.promise, function () {
                pending--;
                return loop();
            });
        });
    }
    loop();

    return function () {
        if (pending <= max) {
            pending++;
            queue.put({
                "this": this,
                "args": Array.prototype.slice.call(arguments)
            });
        }
    }
}


// contrived example

var serialSetTimeout = throttle(2, function (wrap, callback, delay) {
    return setTimeout(wrap(callback), delay);
});

serialSetTimeout(function() { console.log("a"); }, 2000); // t=2s
serialSetTimeout(function() { console.log("b"); }, 1000); // t=3s
serialSetTimeout(function() { console.log("c"); }, 1000); // t=4s
serialSetTimeout(function() { console.log("d"); }, 1000); // dropped!