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EventEmitter.once - events - Node documentation
method EventEmitter.once

Usage in Deno

import { type EventEmitter } from "node:events";
EventEmitter.once<K>(
eventName: Key<K, T>,
listener: Listener1<K, T>,
): this

Adds a one-time listener function for the event named eventName. The next time eventName is triggered, this listener is removed and then invoked.

server.once('connection', (stream) => {
  console.log('Ah, we have our first user!');
});

Returns a reference to the EventEmitter, so that calls can be chained.

By default, event listeners are invoked in the order they are added. The emitter.prependOnceListener() method can be used as an alternative to add the event listener to the beginning of the listeners array.

import { EventEmitter } from 'node:events';
const myEE = new EventEmitter();
myEE.once('foo', () => console.log('a'));
myEE.prependOnceListener('foo', () => console.log('b'));
myEE.emit('foo');
// Prints:
//   b
//   a

Type Parameters

K

Parameters

eventName: Key<K, T>

The name of the event.

listener: Listener1<K, T>

The callback function

Return Type

this