Chaining promises without using 'then'

Question

I have an object (foo) that exposes several methods as promises (using jQuery deferred). The way I did it ended up with this kind of code:

var f         


        

Answer 1

Create your own promise.

function MyPromise(resolver) {
  var _promise = new Promise(resolver);
  this.then = function(onFulfilled, onRejected) {
    var _p = _promise.then(onFulfilled, onRejected);
    return new MyPromise(_p.then.bind(_p));
  };
}

Add whatever methods you want...

MyPromise.prototype.doSomething = function() {
  return this.then(/*...*/);
};

voila!

new MyPromise()
  .then(/*...*/).doSomething()
  .then(/*...*/).doSomething(); // etc...

Bonus:

['resolve', 'reject', 'all'].forEach(function(method) {
  MyPromise[method] = function(...args) {
    var promise = Promise[method](...args);
    return new MyPromise(promise.then.bind(promise));
  };
});

Also in ES6:

class MyPromise {
  constructor(resolver) {
    var _promise = new Promise(resolver);
    this.then = function(onFulfilled, onRejected) {
      var _p = _promise.then(onFulfilled, onRejected);
      return new MyPromise(_p.then.bind(_p));
    };
  }
  doSomething() {
    return this.then(/*...*/);
  }
}