Backoff AJAX requests

backoff-request.js

/**
 * @flow
 */

import request from 'lib/request';

type F<T> = (response: T) => bool;

const BACKOFF_MAX = 60; // seconds
const BACKOFF_ATTEMPTS = 60;

function decay(count: number): number {
  if (count <= 0) {
    return 0;
  }

  return Math.min(BACKOFF_MAX, count * 1.4);
}

export function backoff<R>(predicate: F<R>, args: Object): { cancel: () => void, promise: Promise<R> } {
  let isCancelled = false;

  const promise = new Promise((resolve, reject) => {
    let attempts = 0;
    let backoffValue = 1;

    function run() {
      attempts += 1;

      request(args).then(response => {
        if (predicate(response)) {
          return resolve(response);
        }
        else if (isCancelled == true) {
          return reject({ isCancelled });
        }

        reRun();
      }, error => {
        if (attempts === BACKOFF_ATTEMPTS) {
          return reject(error);
        }
        else if (isCancelled == true) {
          return reject({ isCancelled });
        }

        reRun();
      });
    }

    function reRun() {
      backoffValue = decay(backoffValue);
      setTimeout(run, backoffValue * 1000);
    }

    run();
  });

  return {
    cancel() {
      isCancelled = true;
    },
    promise
  };
}