Create a js promise with a timeout

promiseWithTimeout.js

/**
 * Creates a promise that rejects after the specified amount of time.
 * This can be used with the Promise.race() method to set a timeout on a different Promise:
 * 
 *  Promise.race([
 *      fetchDataSlowly(),
 *      timeoutThenReject(5000)
 *  ]);
 * 
 * @param durationMillis  Number of milliseconds to wait before resolving with a rejection.
 * @returns {Promise}
 */
timeoutThenReject(durationMillis) {
    return new Promise((resolve, reject) => {
        let timeoutId = setTimeout(() => {
            clearTimeout(timeoutId);
            reject('Timed out');
        }, durationMillis);
    });
}

/**
* Apply a timeout to an existing promise.  If the promise doesn't resolve before the timeout, then
* this `promiseWithTimeout` promise will resolve with a rejected status.
*
* @param externalPromise  A promise that won't be allowed to run longer than the specified timeout.
* @param durationMillis  Number of milliseconds to wait before resolving with a rejection.
* @returns {Promise}
**/
export default promiseWithTimeout(externalPromise, durationMillis) {
  return Promise.race([
    externalPromise,
    timeoutThenReject(durationMillis),
  ]);
}