Make Cancellable Promise

make-cancellable.js

Promise.makeCancellable = promise => {
  const deferred = {};
  const promise = new Promise((resolve, reject) => {
    deferred.reject = reject;

    // Invoke the fetch argument with the matching args... only resolve if not
    // aborted.
    promise
      .then(resp => !deferred.aborted && resolve(resp))
      .catch(ex => !deferred.aborted && reject(ex));
  });

  promise.abort = function() {
    deferred.reject(null);
    deferred.aborted = true;
    return promise;
  };

  return promise;
};

// Usage...
Promise.makeCancellable(fetch('/someurl')).then(handleResponse).catch(ex => {
  // Only handle real errors...
  if (ex !== null) {
    throw ex;
  }
});