Queue

example.js

function job(done) {
    console.log('working hard...');

    setTimeout(function () {
        done();
    }, 1000);
}

var queue = new Queue();
queue.add(job, true);
queue.add(job, true);
queue.dispatch();

setTimeout(function () {
    queue.add(job);
    queue.add(job);
}, 200)

queue.js

var Queue = function () {
    this.running = false;
    this.jobs = [];

    this._dispatchNextJob = this._dispatchNextJob.bind(this);
};

Queue.prototype.dispatch = function() {
    if (this.running) {
        return;
    }
    console.log('dispatch');
    this._dispatchNextJob();
};

Queue.prototype._dispatchNextJob = function() {
    if (!this.jobs[0]) {
        this.running = false;
        return;
    }

    this.running = true;
    this.jobs.shift()(this._dispatchNextJob);
};

Queue.prototype.add = function(callback, defer) {
    this.jobs.push(callback);
    if (!defer) {
        this.dispatch();
    }
};