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

emitter.prependOnceListener(eventName, listener)

Prepend a one-time listener function for the event named eventName to the beginning of the listeners array.

HelloWorld.js

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

var emitter = new EventEmitter();

emitter.on('sayHello', () => {
 console.log('Hello Visitor');
});

console.log('Emitting "sayHello" event');
emitter.emit('sayHello');

console.log('\nPrepended another listener function to the event "sayHello"');

emitter.prependOnceListener('sayHello', (stream) => {
 console.log('Good Morning!!!!!!!');
});

console.log('\nEmitting "sayHello" event');
emitter.emit('sayHello');

console.log('\nEmitting "sayHello" event');
emitter.emit('sayHello');

Output

Emitting "sayHello" event
Hello Visitor

Prepended another listener function to the event "sayHello"

Emitting "sayHello" event
Good Morning!!!!!!!
Hello Visitor

Emitting "sayHello" event
Hello Visitor

Note

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

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