Catch unhandled Promise errors

Catch unhandled Promise errors by listening for unhandledrejection events.

• Tracking unhandled rejected Promises
• Translator: Fundebug

In order to ensure readability, free translation rather than literal translation is used in this paper, and a lot of modifications are made to the source code. In addition, the copyright of this article belongs to the original author, and translation is for study only.

When writing asynchronous code with Promise, use reject to handle errors. Sometimes, developers often overlook this and errors go unhandled. Such as:

Function main() {asyncFunc().then(···).then(() => console.log('Done! ')); }Copy the code

Because no catch method is used to catch errors, the asyncFunc() function reject throws errors that are not processed.

This blog post will show you how to catch unhandled Promise errors in the browser and node.js, respectively.

Unhandled Promise error in browser

unhandledrejection

Listen for unhandledrejection events to catch unhandled Promise errors:

Window. The addEventListener (' unhandledrejection 'event = >...);Copy the code

This event is an instance of PromiseRejectionEvent, which has two of the most important properties:

• promisePromise: reject
• reason: Reject value of Promise

Sample code:

window.addEventListener('unhandledrejection', event => { console.log(event.reason); // Prints "Hello, Fundebug!" }); function foo() { Promise.reject('Hello, Fundebug! '); } foo();Copy the code

Fundebug’s JavaScript error monitoring plug-in listens for unHandledrejection events, so it can automatically catch unprocessed Promise errors.

rejectionhandled

Window. The addEventListener (' rejectionhandled 'event = >...);Copy the code

window.addEventListener('unhandledrejection', event => { console.log(event.reason); // Prints "Hello, Fundebug!" }); window.addEventListener('rejectionhandled', event => { console.log('rejection handled'); // After 1 second print "rejection handled"}); function foo() { return Promise.reject('Hello, Fundebug! '); } var r = foo(); setTimeout(() => { r.catch(e =>{}); }, 1000);Copy the code

Unhandled Promise error in Node.js

Listen for unhandledRejection events to catch unhandled Promise errors:

Process. on('unhandledRejection', (reason, promise) => ···);Copy the code

Sample code:

process.on('unhandledRejection', reason => { console.log(reason); // Prints "Hello, Fundebug!" }); function foo() { Promise.reject('Hello, Fundebug! '); } foo();Copy the code

Note: Node.js v6.6.0+ reports unhandled Promise errors by default, so it’s ok not to listen for unhandledrejection events.

Fundebug’s Node.js error monitoring plug-in listens for unhandledRejection events, so it can automatically catch unprocessed Promise errors.

reference