SOURCE

class EventEmitter {
 constructor(){
   this.listeners = []
 }
  on(eventName,func){
    const callbacks = this.listen[eventName] || []
    callbacks.push(func);
    this.listeners[eventName]=callbacks
    
  }
  off(eventName,func){
    
  }
  emit(eventName,...args){
    const callbacks = this.listens[eventName]
    if(callbacks.length>0){
      callbacks.forEach((callback)=>{
        
        callback(...args)
      })
    }
  }
}