Function.prototype.queue

queue.js

var queue = function(f) {
  var queue = [];
  var running = false;

  var initiate = function() {
    if (running || queue.length == 0) {
      return;
    }

    running = true;

    var head = queue[0];
    var callback = head.arguments[head.arguments.length-1];

    queue = queue.slice(1);

    head.arguments[head.arguments.length-1] = function() {
      callback.apply(this, arguments);
      running = false;
      initiate();
    };

    f.apply(head.context, head.arguments);
  };

  return function() {
    queue.push({ context: this, arguments: arguments });
    initiate();
  };
};

Function.prototype.queue = function() {
  return queue(this);
};




var f1 = function(x, callback) {
  setTimeout(function() {
    console.log(x);
    callback();
  }, Math.random() * 1000);
};

var f2 = function(x, callback) {
  console.log(x);
  callback();
};





var noop = function() {};

f1 = f1.queue();
f2 = f2.queue();


f1(1, noop);
f1(2, noop);
f1(3, noop);
f1(4, noop);
f1(5, noop);