EventEmitter初版
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| class EventEmitter{
constructor(){
this.events={}
}
on(type,listener){
if(!this.events[type]){
this.events[type]=[]
}
this.events[type].push(listener)
}
emit(type,...args){
this.events[type].forEach(listener=>{
listener.call(this,...args)
})
}
off(type,listener){
if(this.events[type]){
const index=this.events[type].indexOf(listener)
if(index!==-1){
this.events[type].splice(index,1)
}
}
}
once(type,listener){
const onceListener=(...args)=>{
listener.call(this,...args)
this.off(type,onceListener)
}
this.on(type,onceListener)
}
}
|
测试
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| const eventEmitter=new EventEmitter()
const listener=(args)=>{
console.log(args);
}
eventEmitter.once('test',listener)
eventEmitter.off('test',listener)
eventEmitter.emit('test',{a:1})
|
执行上述代码，会发现test事件被触发了一次，预期应该是不执行的，因为off了。解决办法如下。
once失效
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| ...
off(type,listener){
if(this.events[type]){
const index=this.events[type].findIndex(l=>l.fn===listener||l===listener)
if(index!==-1){
this.events[type].splice(index,1)
}
}
}
...
once(type,listener){
const onceListener=(...args)=>{
listener.call(this,...args)
this.off(type,onceListener)
}
onceListener.fn=listener
this.on(type,onceListener)
}
|
写在最后
多看源码