ES6 Cancellable Promise Wrapper

promise-cancellable.js

/**
 * Returns a promise that has a cancelled method that will cause the callbacks not to fire when it resolves or rejects
 * @param promise to wrap
 * @returns new promise that will only resolve or reject if cancel is not called
 */
export default function cancellable(promise) {
  var cancelled = false;

  const toReturn = new Promise((resolve, reject) => {
    promise.then(() => {
      if (!cancelled) {
        resolve.apply(this, arguments);
      }
    }, () => {
      if (!cancelled) {
        reject.apply(this, arguments);
      }
    })
  });

  toReturn.cancel = () => cancelled = true;
  return toReturn;
};

This simple function takes a promise and returns a new promise that will not resolve or reject if cancelled.