08慕课网《进击Node.js基础》事件events

Posted 2020-11-09 言凡

引用events模块中的EventEmitter 

事件的监听和发射

相同的事件发射数量有限，可以通过setMaxListeners设置峰值

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

var life = new EventEmitter()
//加不加都没有报警告
//life.setMaxListeners(10)

life.on(\'clickEvent\',function(who){
    console.log(\'给\' + who + \' 倒水\')
})

life.emit(\'clickEvent\',\'汉子1\')

每个emit都有返回值，表示是否有相应的监听事件

var hasClickListener = life.emit(\'clickEvent\',\'汉子12\')
var hasChangeListener = life.emit(\'changeEvent\',\'妹子1\')

 console.log(hasClickListener)
 console.log(hasChangeListener)
 console.log(hasPutListener)

 取消监听

//可以放到 on 和 emit 后面
function water(who){
    console.log(\'给 \' + who + \' 倒水\')
}

life.on(\'changeEvent\',water)
//还没有被取消，emit不能放到 on之前
life.emit(\'changeEvent\',\'张三\')
//water不可以用匿名函数，removeListener需要在emit之前
life.removeListener(\'changeEvent\',water)
//移除所有监听，可以传递事件名作为参数
//life.removeAllListeners()


var hasChangeListener = life.emit(\'changeEvent\',\'妹子1\')//监听被取消
var hasPutListener = life.emit(\'clickEvent\',\'李白\')
// //是否被监听
 console.log(hasChangeListener)
 console.log(hasPutListener)

 监听数量

console.log(\'changeEvent：\' + life.listeners(\'changeEvent\').length)
console.log(\'clickEvent：\' + life.listeners(\'clickEvent\').length)
console.log(\'all：\' + life.listeners.length)
//EventEmitter提供的方法
console.log(\'EventEmitter提供：\')
console.log(\'changeEvent:\' + EventEmitter.listenerCount(life,\'changeEvent\'))
console.log(\'clickEvent:\' + EventEmitter.listenerCount(life,\'clickEvent\'))