An alternative playground with cancel-able Promises that rejects through arbitrary value

Promise-rejet.js

(function (Object, Original) {'use strict';

  // (C) Andrea Giammarchi - WTFPL

  OP = Original.prototype;
  if ('cancel' in OP) return;

  var
    OP,
    $then = OP.then,
    $catch = OP.catch,
    defineProperty = Object.defineProperty,
    defineProperties = Object.defineProperties,
    // noop = function () {},
    createDescriptors = function (cancel) {
      var descriptors = {
        'cancel': {value: function () {
          // this.catch(noop);
          return cancel.apply(this, arguments);
        }},
        'then': {value: function (ok, err) {
          var args = arguments.length === 2 ? [ok, err] : [ok];
          if (typeof ok === 'function') args[0] = function () {
            var r = ok.apply(this, arguments);
            if (
              r instanceof Original &&
              r.hasOwnProperty('cancel')
            ) {
              cancel = r.cancel;
            }
            return r;
          };
          return defineProperties(
            $then.apply(this, args),
            descriptors
          );
        }},
        'catch': {value: function () {
          return defineProperties(
            $catch.apply(this, arguments),
            descriptors
          );
        }}
      };
      return descriptors;
    }
  ;

  function Promise(callback) {
    var
      resolve, reject, cancel,
      state = 'pending',
      p = new Original(function ($resolve, $reject) {
        resolve = $resolve;
        reject = $reject;
      })
    ;
    callback(
      function () {
        if (state === 'pending') {
          state = 'resolved';
          resolve.apply(this, arguments);
        }
      },
      function () {
        if (state === 'pending') {
          state = 'rejected';
          reject.apply(this, arguments);
        }
      },
      function (howToCancel) {
        if (typeof howToCancel !== 'function') {
          throw new Error('Unable to cancel this promise');
        }
        return cancel || (cancel = function () {
          if (state === 'pending') {
            state = 'canceled';
            howToCancel.apply(this, arguments);
            reject.apply(this, arguments);
            return this;
          }
        });
      }
    );
    return cancel ? defineProperties(p, createDescriptors(cancel)) : p;
  }

  Object.getOwnPropertyNames(Original).forEach(function (name) {
    if (!(name in Promise)) {
      defineProperty(
        Promise,
        name,
        Object.getOwnPropertyDescriptor(Original, name)
      );
    }
  });

  Promise.prototype = OP;

  defineProperty(OP, 'cancel', {
    configurable: true,
    enumerable: false,
    writable: true,
    value: function () { return this; }
  });

  try {
    module.exports = Promise;
  } catch(e) {
    this.Promise = Promise;
  }

}.call(this, Object, Promise));