Summary  
This chapter covers how to handle unhandled Promise rejections by ensuring every Promise has a `.catch()` handler or is wrapped in a `try/catch` when using `async/await` to prevent unexpected process termination.

General domain of usage  
Server-side JavaScript applications

When working with Promises in Node.js, it is important to handle every possible rejection. If a Promise is rejected and there is no handler—such as a `.catch()` method or a `try/catch` block when using `async/await`—the rejection is considered unhandled. Unhandled Promise rejections can cause your application to behave unpredictably. In earlier versions of Node.js, unhandled rejections would only log a warning, but in more recent versions, they may cause the process to terminate. This can lead to downtime, lost data, or security risks if not addressed.

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In large Node.js applications, you can listen for unhandled Promise rejections globally to help with debugging or logging. This is especially useful in development environments.
```js
process.on('unhandledRejection', (reason, promise) => {
  console.error('Unhandled Rejection:', reason);
});
```
This event lets you detect unhandled rejections, but it should **not** be used as a replacement for proper `.catch()` or `try/catch` handling. Always handle rejections explicitly in your code to prevent unexpected crashes in production.

Note

What is a possible consequence of leaving a Promise rejection unhandled in recent versions of Node.js?

Understand how Node.js manages asynchronous operations and concurrency through its event loop. Explore callbacks, Promises, and async/await to control complex asynchronous flows with clarity. Apply modern patterns and best practices to write efficient, non-blocking, and resilient JavaScript for real-world Node.js applications.

Explore how Node.js handles multiple tasks without blocking execution. Examine the event loop, its phases, and the mechanisms that enable asynchronous behavior, including timers, nextTick, and setImmediate.

Work with Node.js asynchronous APIs and understand how they interact with the event loop. Transition from traditional callbacks to Promises, managing asynchronous operations more predictably and with cleaner code.

Simplify asynchronous workflows with async/await syntax and handle errors gracefully. Avoid common pitfalls like callback hell, manage unhandled rejections, and apply proven strategies for writing reliable, maintainable asynchronous code.

Handling Unhandled Promise Rejections

Awesome!

Handling Unhandled Promise Rejections