Node.js Event Emitters Get the number of listeners registered to listen for a specific event
Example
The function Emitter.listenerCount(eventName) will return the number of listeners that are currently listening for the event provided as argument
const EventEmitter = require("events");
class MyEmitter extends EventEmitter{}
var emitter = new MyEmitter();
emitter
.on("data", ()=>{ // add listener for data event
console.log("data event emitter");
});
console.log(emitter.listenerCount("data")) // => 1
console.log(emitter.listenerCount("message")) // => 0
emitter.on("message", function mListener(){ //add listener for message event
console.log("message event emitted");
});
console.log(emitter.listenerCount("data")) // => 1
console.log(emitter.listenerCount("message")) // => 1
emitter.once("data", (stuff)=>{ //add another listener for data event
console.log(`Tell me my ${stuff}`);
})
console.log(emitter.listenerCount("data")) // => 2
console.log(emitter.listenerCount("message"))// => 1
