SOURCE

class EventBus {
//    {
//        key1:[
//             {fn:fn1,isOnce:false},
//             {fn:fn2,isOnce:false},
//             {fn:fn3,isOnce:true}
//            ]
//    }
    constructor(){
        this.events={}
    }
    on(type,fn,isOnce=false){
        const events = this.events;
        if(!events[type]){
            events[type]=[]
        }
        events[type].push({fn,isOnce})

    } // 绑定
    once(type,fn,isOnce=true){
        this.on(type,fn,isOnce);
    } //绑定一次
    off(type,fn){
        if(!fn){
            this.events[type]=[];
        }else{
            const fnList = this.events[type];
            if(fnList){
                this.events[type] = fnList.filter((item)=>item.fn !==fn)
            }
        }

    } //解绑
   
    trigger(type,...args){
        const fnList = this.events[type];
        if(!fnList) {return} ;
        this.events[type] = fnList.filter((item)=>{
            const {fn,isOnce} = item;
            fn(...args);
            if(!isOnce){ return true } //isOnce 为false
            return false
        })

    }//触发事件
}
;

const e = new EventBus();
function fn1(a,b){
    console.log('fn1',a,b)
}
function fn2(a,b){
    console.log('fn2',a,b)
}
function fn3(a,b){
    console.log('fn3',a,b)
}
e.on('key1',fn1);
e.on('key1',fn2);
e.once('key1',fn3);
e.trigger('key1',1,2);
e.off('key1',fn1);
e.trigger('key1',3,4);