Chaining delays in JavaScript (setTimeout) using Promises (ie. delay(func1, 1000).delay(func2, 1000).delay(func3, 1000))

delayPromise.js

/**
 * Daisy chaining delays (setTimeout) using Promises
 *
 * Ex: delay(func1, 1000).delay(func2, 1000).delay(func3, 1000);
 *
 * @param {Function} cb - Callback function
 * @param {Number} ms - Time delay (in milliseconds)
 * @return chainable delay Promise (ie. delay(cb, ms).delay(cb, ms).delay(cb, ms)...)
 *
 * @see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Using_promises#Creating_a_Promise_around_an_old_callback_API
 * @see http://2ality.com/2013/03/subclassing-builtins-es6.html
 * @see https://stackoverflow.com/a/6921279/933951
 * @see https://gist.github.com/domenic/8ed6048b187ee8f2ec75#file-angularpromise-js-L20
 */

function delay (cb, ms) {

  // MyPromise constructor - subclass of Promise
  function MyPromise(fn) {
    var promise       = new Promise((resolve, reject) => fn(resolve, reject));
    promise.__proto__ = MyPromise.prototype;
    return promise;
  }

  // MyPromise should extend Promise
  MyPromise.__proto__           = Promise;
  MyPromise.prototype.__proto__ = Promise.prototype;

  // Extend MyPromise to return delay from promise success
  MyPromise.prototype.delay = function (cb, ms) {
    return this.then( () => delay(cb, ms) );
  }
  
  // Create internal 'wait' promise using setTimeout
  let _wait = ms => new MyPromise( resolve => setTimeout(resolve, ms) );

  return _wait(ms).then(cb);

}

Hi, thanks for this. But my problem is deeper.

Suppose delay is a method in a class, then how will you do it?
I was trying to implement delay in this library url-request.