EventEmitter.listenerCount(emitter, eventName)

• emitter <EventEmitter> 要查询的触发器
• eventName <string> | <symbol> 事件名称

返回在给定 emitter 上注册的给定 eventName 的监听器数量的类方法。

const myEmitter = new MyEmitter();
myEmitter.on('event', () => {});
myEmitter.on('event', () => {});
console.log(EventEmitter.listenerCount(myEmitter, 'event'));
// 打印: 2

• emitter <EventEmitter> The emitter to query
• eventName <string> | <symbol> The event name

A class method that returns the number of listeners for the given eventName registered on the given emitter.

const myEmitter = new MyEmitter();
myEmitter.on('event', () => {});
myEmitter.on('event', () => {});
console.log(EventEmitter.listenerCount(myEmitter, 'event'));
// Prints: 2