exponentialRandomBackoff.ts

export function exponentialRandomBackoff(
  initialIntervalMillis: number,
  multiplier: number,
  randomizationFactor: number
) {
  checkInterval(initialIntervalMillis);
  checkMultiplier(multiplier);
  checkRandomizationFactor(randomizationFactor);
  return (attemptsMade: number) => {
    const interval = Math.round(Math.pow(multiplier, attemptsMade) * initialIntervalMillis);
    return randomize(interval, randomizationFactor);
  };
}

function randomize(current: number, randomizationFactor: number): number {
  let delta = randomizationFactor * current;
  let min = current - delta;
  let max = current + delta;

  return min + Math.random() * (max - min + 1);
}

function checkInterval(interval: number) {
  if (interval < 10) {
    throw new RangeError('Illegal argument interval: ' + interval + ' millis');
  }
}

function checkMultiplier(multiplier: number) {
  if (multiplier < 1.0) {
    throw new RangeError('Illegal argument multiplier: ' + multiplier);
  }
}

function checkRandomizationFactor(randomizationFactor: number) {
  if (randomizationFactor < 0.0 || randomizationFactor >= 1.0) {
    throw new RangeError('Illegal argument randomizationFactor: ' + randomizationFactor);
  }
}