emitter.once(eventName, listener)
eventName
<string> | <symbol> 事件的名称。listener
<Function> 回调函数- 返回: <EventEmitter>
为名为 eventName
的事件添加单次的 listener
函数。
下次触发 eventName
时,将移除此监听器,然后再调用。
server.once('connection', (stream) => {
console.log('Ah, we have our first user!');
});
返回对 EventEmitter
的引用,以便可以链式调用。
默认情况下,事件监听器按添加顺序调用。
emitter.prependOnceListener()
方法可用作将事件监听器添加到监听器数组开头的替代方法。
import { EventEmitter } from 'node:events';
const myEE = new EventEmitter();
myEE.once('foo', () => console.log('a'));
myEE.prependOnceListener('foo', () => console.log('b'));
myEE.emit('foo');
// 打印:
// b
// a
const EventEmitter = require('node:events');
const myEE = new EventEmitter();
myEE.once('foo', () => console.log('a'));
myEE.prependOnceListener('foo', () => console.log('b'));
myEE.emit('foo');
// 打印:
// b
// a
eventName
<string> | <symbol> The name of the event.listener
<Function> The callback function- Returns: <EventEmitter>
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
const EventEmitter = require('node:events');
const myEE = new EventEmitter();
myEE.once('foo', () => console.log('a'));
myEE.prependOnceListener('foo', () => console.log('b'));
myEE.emit('foo');
// Prints:
// b
// a