expo-notifications/src/utils/backoff.ts

Provides an API to fetch push notification tokens and to present, schedule, receive, and respond to notifications.

// See: https://github.com/ide/backoff/blob/0c83ac6/src/backoff.ts
export function computeNextBackoffInterval(
  initialBackoff: number,
  previousRetryCount: number,
  {
    multiplier = 1.5,
    randomizationFactor = 0.25,
    minBackoff = initialBackoff,
    maxBackoff = Infinity,
  } = {}
): number {
  // NOTE: These are internal assumptions/assertions of the backoff function, but we're hardcoding
  // these values, so they're replaced with conditions instead, to make this self-documenting

  // The initial backoff interval must be positive
  if (initialBackoff <= 0) initialBackoff = 1;
  // The previous retry count must not be negative
  if (previousRetryCount < 0) previousRetryCount = 0;
  // The backoff multiplier must be greater than or equal to 1
  if (multiplier < 1) multiplier = 1;
  // The minimum backoff interval must be positive
  if (randomizationFactor < 0 || randomizationFactor > 1) randomizationFactor = 0;

  const nextBackoff = initialBackoff * multiplier ** previousRetryCount;
  // Apply jitter within the negative to positive range of the randomization factor
  const jitterFactor = 1 - randomizationFactor + 2 * randomizationFactor * Math.random();

  return Math.min(Math.max(nextBackoff * jitterFactor, minBackoff), maxBackoff);
}