1. 为事件添加监听器两种方式
    2. 如何处罚事件监听器
    3. 查询事件监听器数量
    4. 如何取消事件监听器 ```javascript var event = require(‘events’) var eventEmitter = new event.EventEmitter()

    var handler1 = () => { console.log(‘handler1’) }

    var handler2 = () => { console.log(‘handler2’) }

    eventEmitter.on(‘changqing’, handler1)

    eventEmitter.addListener(‘changqing’, handler2)

    eventEmitter.emit(‘changqing’)

    console.log(eventEmitter.listenerCount(‘changqing’))

    eventEmitter.removeListener(‘changqing’, handler1)

    eventEmitter.emit(‘changqing’)

    console.log(eventEmitter.listenerCount(‘changqing’)) ```