// CLICK PREVIEW!

​

Queue = [];

Queue.execute = function () {

  if (Queue.length)

    Queue.shift()(Queue.execute);

  else 

    Queue.last();

};

​

Queue.last = function() {

  console.log("end");

};

Queue.push(function(callback){

  console.log("1");

  callback();

});

Queue.push(function(callback){

  console.log("2");

  callback();

});

Queue.push(function(callback){

  console.log("3");

  callback();

});

Queue.push(function(callback){

  console.log("4");

  callback();

});

Queue.execute();

​