Exponential backoff retry logic for a function that returns a Promise

attemptWithRetry.js

/**
 * Retries a function that returns a promise a given number of times and backs
 * off each attempt exponentially.
 *
 * @param {Function} promiseGenerator The function to retry.
 * @param {number} [attempts=5] Number of attempts to make.
 * @param {number} [delay=1000] Initial delay between attempts in ms.
 * @return {Promise}
 */
function attemptWithRetry(promiseGenerator, attempts = 5, delay = 100) {
  return new Promise((resolve, reject) => {
    promiseGenerator()
      .then(resolve)
      .catch((error) => {
        if (attempts > 1) {
          setTimeout(() => {
            resolve(
              attemptWithRetry(promiseGenerator, attempts - 1, delay * 2)
            );
          }, delay);
        } else {
          reject(error);
        }
      });
  });
}

// Example:
//
// function coinFlip () {
//   return Math.floor(Math.random() * 2) === 0
// }
//
// function failHalfTheTime () {
//   return new Promise((resolve, reject) => {
//     coinFlip() ? resolve() : reject()
//   })
// }
//
// attemptWithRetry(failHalfTheTime)
//   .then(() => console.log('success'))
//   .catch(() => console.error('error'))

Renamed fn to promiseGenerator.