Exponential backoff scheduler to be used with RxJS's retrywhen

exponentialBackOffScheduler.js

// https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/retrywhen.md

function exponentialBackOffScheduler(options) {
  return function(errors) {
    return errors.scan(options, function(currentOptions, err) {
      if (currentOptions.maxRetries <= 0) {
        throw err;
      }
      return {
        maxRetries: currentOptions.maxRetries - 1,
        delay: currentOptions.delay * 2,
      };
    })
    .map(_.property('delay'))
    .scan(0, add)
    .map(waitUntil)
    .flatMap(_.identity);
  }

  function waitUntil(delay) {
    return Rx.Observable.interval(delay).take(1);
  }

  function add(a, b) {
    return a + b;
  }
}