模块概览
events模块是node的核心模块之一,几乎所有常用的node模块都继承了events模块,比如http、fs等。
模块本身非常简单,API虽然也不少,但常用的就那么几个,这里举几个简单例子。
基础例子
下面一共是6个例子,都非常简单,可以直接拷贝出来运行。例子5比较有意思,虽然也并不复杂,但确实是容易记错的点,感兴趣的同学可以看下。
例子1:单个事件监听器
var EventEmitter = require('events'); class Man extends EventEmitter {} var man = new Man(); man.on('wakeup', function(){ console.log('man has woken up'); }); man.emit('wakeup'); // 输出如下: // man has woken up
例子2:同个事件,多个事件监听器
可以看到,事件触发时,事件监听器按照注册的顺序执行。
var EventEmitter = require('events'); class Man extends EventEmitter {} var man = new Man(); man.on('wakeup', function(){ console.log('man has woken up'); }); man.on('wakeup', function(){ console.log('man has woken up again'); }); man.emit('wakeup'); // 输出如下: // man has woken up // man has woken up again
例子3:只运行一次的事件监听器
var EventEmitter = require('events'); class Man extends EventEmitter {} var man = new Man(); man.on('wakeup', function(){ console.log('man has woken up'); }); man.once('wakeup', function(){ console.log('man has woken up again'); }); man.emit('wakeup'); man.emit('wakeup'); // 输出如下: // man has woken up // man has woken up again // man has woken up
例子4:注册事件监听器前,事件先触发
可以看到,注册事件监听器前,事件先触发,则该事件会直接被忽略。
var EventEmitter = require('events'); class Man extends EventEmitter {} var man = new Man(); man.emit('wakeup', 1); man.on('wakeup', function(index){ console.log('man has woken up ->' + index); }); man.emit('wakeup', 2); // 输出如下: // man has woken up ->2
例子5:异步执行,还是顺序执行
例子很简单,但非常重要。究竟是代码1先执行,还是代码2先执行,这点差异,无论对于我们理解别人的代码,还是自己编写node程序,都非常关键。
实践证明,代码1先执行了。(node v6.1.0)
var EventEmitter = require('events'); class Man extends EventEmitter {} var man = new Man(); man.on('wakeup', function(){ console.log('man has woken up'); // 代码1 }); man.emit('wakeup'); console.log('woman has woken up'); // 代码2 // 输出如下: // man has woken up // woman has woken up
例子6:移除事件监听器
var EventEmitter = require('events'); function wakeup(){ console.log('man has woken up'); } class Man extends EventEmitter {} var man = new Man(); man.on('wakeup', wakeup); man.emit('wakeup'); man.removeListener('wakeup', wakeup); man.emit('wakeup'); // 输出如下: // man has woken up
相关链接