gistfile1.js

var Bluebird = require('bluebird');

function Something() {
  this.queue = [];
  this.currentJob = null;
}

Something.prototype.queueJob = function (job) {
  if (this.currentJob) {
    this.queue.push(job);
  } else {
    this.currentJob = Bluebird.bind(this)
    .then(job)
    .then(function () {
      this.currentJob = null;
      if (this.queue.length) {
        var self = this;
        setImmediate(function () {
          self.queueJob(self.queue.shift());
        });
      }
    });
  }
};

Something.prototype.sayHello = function () {
  this.queueJob(function () {
    return new Bluebird(function (resolve, reject) {
      setTimeout(function () {
        console.log('Hello');
        resolve();
      }, 500);
    });
  });
  return this;
};

Something.prototype.sayHello2 = function () {
  this.queueJob(function () {
    return new Bluebird(function (resolve, reject) {
      setTimeout(function () {
        console.log('Hello2');
        resolve();
      }, 500);
    });
  });
  return this;
};


var thing = new Something();

thing.sayHello().sayHello().sayHello2().sayHello2().sayHello();