Node.js Process unhandledPromiseRejection Event24 Feb 2025 | 4 min read Using the robust runtime environment, Node.js allows developers to execute JavaScript on the server side. It is renowned for being event-driven, and it is built on the V8 JavaScript engine found in Chrome. The non-blocking input/output paradigm makes Node.js effective and lightweight. It is ideal for developing network applications that scale. Working with Node.js requires a thorough grasp of how it manages promises. It is especially true when working with asynchronous processes. What are Node.js promises?Asynchronous JavaScript operations may now be managed with promises. Compared with standard callback methods, they offer a more organized and controllable method of handling asynchronous code. A task that is anticipated to be finished in the future is represented by a promise. One of three states pending, fulfilled or rejected may apply to it. A promise that comes true, which indicates the procedure went well. It produced the desired outcome in the console. When an operation fails, it is indicated by the rejection of a promise. It usually contains an error object as the cause of the failure. Problem with Unhandled Promise RejectionsWith the advent of async/await syntax in ES2017, promises have become increasingly prevalent in the Node.js context. However, it is a frequent problem when a promise is refused, and no handler is in place to handle that rejection. It is referred to as an unhandled rejection of a promise. When unhandled promise rejection occurs, it means a promise has failed, and no .catch() method or rejection handler was provided to deal with the error. The error's origins might not be immediately obvious, resulting in unexpected behavior and complicating troubleshooting. Node.js Process unhandledRejection EventNode.js provides a global unhandled rejection event to address the issue of unhandled promise rejections, which is processed. Each time a promise is turned down, and no rejection handler is connected throughout the event loop turn, this event is released. Here is a simple example demonstrating the use of the unhandled rejection event. This example defines a callback function to handle the unhandledRejection event. The event is listened for the promise that was denied, and the reason for the rejection are the two inputs to the callback function. One input is often an error object. Handling Unhandled RejectionsA Node.js application may handle unhandled promise rejections globally by using an unhandledRejection event. It can help with resource cleanup, error reporting, and even gentle program shutdown. 1. Employ async/await with try/catch: When utilizing the async/await syntax, enclose the asynchronous code in a try/catch block to manage failures. Output: ![]() 2. Centralized Error Handling: We should consider implementing central error handling logic for larger systems. To do this, we should build utility functions that will handle errors in our application uniformly. Output: ![]() Deprecation and Future ChangesThe way Node.js handles unhandled promise rejections has changed over time. It is important to remember that promise rejections that were not handled were ignored by default in previous iterations of Node.js. Beginning with Node.js 10, logging a warning was the default practice. Subsequent versions have included additional changes. These offer improved tools for managing unhandled promise rejections. With Node.js 15 and later, the --unhandled-rejections command-line option allows us to modify the default action for unhandled promise rejections. This flag may have one of the following values.
Conclusion:In conclusion, one of the most important aspects of developing dependable Node.js apps is managing unhandled promise rejections. Developers may enhance an application's stability by utilizing the unhandledRejection event to detect and address faults on a global scale. It is best practice to deal with promise rejections directly in code and provide error handling that is consistent and predictable. Keeping up with changes in error-handling techniques can help developers. This enables the creation of more robust and high-performing apps as Node.js continues to expand. Next TopicNodejs-process-hrtime-bigint-method |
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