@fortify-ts/fallback

@fortify-ts/fallback

Fallback pattern for the Fortify-TS resilience library.

Installation

npm install @fortify-ts/fallback
# or
pnpm add @fortify-ts/fallback

Features

• Default Values: Return fallback on failure
• Alternative Operations: Execute backup operation on failure
• Custom Predicates: shouldFallback callback
• Notifications: onFallback and onSuccess callbacks

Usage

Basic Usage

import { Fallback } from '@fortify-ts/fallback';

const fallback = new Fallback<User>({
  fallback: () => ({ id: 0, name: 'Guest' }),
});

// Returns Guest user if operation fails
const user = await fallback.execute(async (signal) => {
  return fetchUser(userId, { signal });
});

With Error Context

const fallback = new Fallback<Response>({
  fallback: (error) => {
    console.log(`Falling back due to: ${error.message}`);
    return cachedResponse;
  },
});

Custom Fallback Condition

const fallback = new Fallback<Response>({
  fallback: () => defaultResponse,

  // Only fallback on network errors
  shouldFallback: (error) => {
    return error instanceof NetworkError;
  },
});

Configuration Options

const fallback = new Fallback<Data>({
  // Fallback function (required)
  fallback: (error) => defaultData,

  // Custom fallback condition
  shouldFallback: (error) => error instanceof NetworkError,

  // Notification on fallback
  onFallback: (error) => {
    metrics.increment('fallback.activated');
  },

  // Notification on success
  onSuccess: (result) => {
    metrics.increment('primary.success');
  },

  // Optional logger
  logger: myLogger,
});

Async Fallback

const fallback = new Fallback<Data>({
  fallback: async (error) => {
    // Fallback to cache
    return await cache.get('backup-data');
  },
});

Configuration Reference

Option	Type	Default	Description
fallback	function	required	Fallback function
shouldFallback	function	-	Custom condition
onFallback	function	-	Fallback callback
onSuccess	function	-	Success callback
logger	FortifyLogger	-	Optional logger

License

MIT