自制的event emmiter

export class myEmmiter{
    constructor(){
        this.listeners =[];
        this.laterListeners = [];
    }
    on(event,func){
      if(!this.listeners[event]){
            this.listeners[event] = [];
        }
      if(this.laterListeners.length >0){
        //在有listener之前有emmit的情况
      this.listeners[event].push(func);
        this.laterListeners.forEach((item)=>{
          this.emit(item.event,item.message)
        })
      }
        
        this.listeners[event].push(func);
        
    }
    emit(event,message){
        if(!this.listeners[event]){
            //如果未注册emit了,保存起来先
            let later = {
              event:event,
              message: message
            }
            this.laterListeners.push(later);
            return;
        }
        if(this.listeners[event].length >0){
        this.listeners[event].forEach(element => {
            if(message){
                element(message)
            }
        });
    }
  }
}
//做个单例
let emmiter;
export function getEmmiter(){  
   if(!emmiter){
    emmiter = new myEmmiter();
   }
   return emmiter;
}
export const eventEmmiter = getEmmiter();