关于数据结构:数据结构js实现栈

class Stack {  constructor() {    this.items = [];  }  push(item) {    this.items.push(item);  }  pop() {    return this.items.pop();  }  // 返回顶部元素，然而不批改  peek() {    return this.items.at(-1);  }  isEmpty() {    return this.items.length === 0;  }  clear() {    this.items = [];  }  size() {    return this.items.length;  }  toString() {    if (this.isEmpty()) {      return "";    }    let objString = `${this.items[0]}`;    for (let i = 1; i < this.count; i++) {      objString = `${objString},${this.items[i]}`;    }    return objString;  }}