JavaScript Cancelable Promise

cancelable-promise.js

var CancelablePromise = (function(){
  var cancelledPromiseSymbol = Symbol('PROMISE_CANCELLED');

  function createTypeError(message) {
    var error = new TypeError(message);
    var stack = error.stack.split('\n');
    stack.splice(1, 1);
    stack[1] = stack[1].replace(/:\d+:\d+\)$/, ')');
    error.stack = stack.join('\n');
    throw error;
  }

  function CancelablePromise(callback) {
    if (!(this instanceof CancelablePromise)) {
      throw createTypeError('undefined is not a cancelable promise');
    }
    if (typeof callback !== 'function') {
      throw createTypeError('Promise resolver ' + String(callback) + ' is not a function');
    }

    var resolve;
    var reject;
    var cancelMethod = undefined;

    var returnPromise = new Promise(function(res, rej) {
      resolve = res;
      reject = rej;
    });
    returnPromise.cancel = function() {
      if (!cancelMethod) reject(cancelledPromiseSymbol);
      Promise.resolve().then({ then: cancelMethod }).then(resolve, reject);
    };

    var onCancel = function(cb) {
      if (typeof cb !== 'function') {
        throw createTypeError('Promise onCancel handler ' + String(cb) + ' is not a function');
      }
      cancelMethod = cb;
    };

    callback(resolve, reject, onCancel);
    
    return returnPromise;
  };

  CancelablePromise.name = 'Promise';
  CancelablePromise.prototype = Promise.prototype;
  CancelablePromise.CANCELLED = cancelledPromiseSymbol;
  CancelablePromise.resolve = Promise.resolve;
  CancelablePromise.reject = Promise.reject;
  CancelablePromise.race = Promise.race;

  return CancelablePromise;
}());