EventEmitter

Note

To enable built-in Node.js APIs and polyfills, add the nodejs_compat compatibility flag to your Wrangler configuration file. This also enables nodejs_compat_v2 as long as your compatibility date is 2024-09-23 or later. Learn more about the Node.js compatibility flag and v2.

An EventEmitter is an object that emits named events that cause listeners to be called.

import { EventEmitter } from 'node:events';

const emitter = new EventEmitter();
emitter.on('hello', (...args) => {
  console.log(...args);
});

emitter.emit('hello', 1, 2, 3);

The implementation in the Workers runtime fully supports the entire Node.js EventEmitter API. This includes the captureRejections option that allows improved handling of async functions as event handlers:

const emitter = new EventEmitter({ captureRejections: true });
emitter.on('hello', async (...args) => {
  throw new Error('boom');
});
emitter.on('error', (err) => {
  // the async promise rejection is emitted here!
});

Refer to the Node.js documentation for EventEmitter ↗ for more information.