Resilience4js

Resilience4js is an open-source JavaScript library that provides resilience patterns for building fault-tolerant applications in JavaScript environments, including Node.js and modern browsers. It is inspired by resilience4j, a Java-based library, and aims to deliver similar capabilities in the JavaScript ecosystem. The library focuses on composing fault-tolerance strategies such as circuit breaking, retries, timeouts, bulkheads, and rate limiting to help applications survive transient failures and slow dependencies.

Key components include a circuit breaker to prevent cascading failures by trip and close states; a retry mechanism with configurable backoff; a time limiter to bound operation duration; bulkhead isolation to constrain concurrent calls; and rate limiting to regulate traffic. It supports both promises and async/await flows and can be integrated with common HTTP clients like fetch or axios, as well as custom asynchronous operations. Fallbacks can be defined to provide alternative responses when a protected call fails.

Resilience4js is designed modularly with separate policy objects that can be composed per operation or across an application. Configuration is typically declarative, allowing users to specify thresholds, time windows, and backoff strategies. The library emits events or metrics to help observe health and performance, and it can be extended with custom listeners.

Developers can install via npm and import the relevant modules. The project encourages non-blocking patterns and provides adapters to work with existing codebases. It aligns with general resilience practices used in cloud-native and microservice architectures.

See also resilience4j, Polly, Hystrix (legacy).