node.js: emitter.once(eventName, listener)

emitter.once(eventName, listener)

This method adds one-time listener to this event. Even though the event emitted more than one time, this listener called only once.

HelloWorld.js

var EventEmitter = require('events').EventEmitter;

var emitter = new EventEmitter();

emitter.once('sayHello', (name) => {
 console.log("Hello mr.%s, How are you?", name);
});

/* Emitting 'sayHello' event 3 times */
emitter.emit('sayHello', "Krishna");
emitter.emit('sayHello', "Krishna");
emitter.emit('sayHello', "Krishna");

Output

Hello mr.Krishna, How are you?

Note

a.   This method returns a reference to the EventEmitter, so that calls can be chained.

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