JavaScript) 스택 Stack

class Node{
  constructor(item){
    this.item = item;
    this.next = null;
  }
}

class Stack{
  constructor(){
    this.topOfStack = null;
    this.length = 0;
  }

  push(item){
    const node = new Node(item);
    if(this.topOfStack!=null){
      node.next = this.topOfStack; 
    }
      this.topOfStack = node;
      this.length+=1;
  }

  pop(){
    if(this.length==0)return -1;
    const popItem = this.topOfStack;
    this.topOfStack = popItem.next;
    this.length-=1;

    return popItem.item
  }

  size(){
    return this.length;
  }

  empty(){
    if(this.length==0) return 1;
    else return 0;
  }

  top(){
    if(this.length==0)return -1;
    return this.topOfStack.item; 
  }

}