问这个Queue类有什么问题？Javascript

EN

class Queue{
   // Array is used to implement a Queue
    constructor(){
        this.items = {};
        this.count = 0;
    }

    // enqueue(item)
    enqueue(element){    
        // adding element to the queue
        this.items.push(element);
        this.count++;
    }
    // dequeue()
    dequeue(){
        // removing element from the queue
        // returns underflow when called 
        // on empty queue
        if(this.isEmpty())
            return "Underflow";
        this.count--;
        return this.items.shift();
     }

    // front()
    front(){
        // returns the Front element of 
        // the queue without removing it.
        if(this.isEmpty())
            return "No elements in Queue";
        return this.items[0];
    }

    isEmpty(){
        // return true if the queue is empty.
        return this.items.length == 0;
    }

    // peek()
    peek(){
        return this.items[this.count]
    }

    size(element){
        return this.count;
    }

    show(){
        var result = '';
        var i=this.count-1;

        for(i; i>=0; i--){
            result += this.items[i] +' ';
        }

        return result;
    }
}