Build a stack class

The challenge

Write a class Stack with methods push(item), pop() (removes and returns the top item, or undefined if empty), peek() (returns the top item without removing it), and a getter size. Keep the items in a private field.

Try it

Write your answer below, then press Check my answer. Your code runs right here in your browser, and the tests tell you what works.

What the tests check

• Pop returns the last item pushed: (() => { const s = new Stack(); s.push(1); s.push(2); return [s.pop(), s.size]; })() gives [2, 1]
• Peek doesn’t remove: (() => { const s = new Stack(); s.push("a"); return [s.peek(), s.size]; })() gives ["a", 1]
• Popping an empty stack gives undefined: new Stack().pop() gives undefined
• The items are private: Object.keys(new Stack()).length gives 0

Hints

Stuck? Open one hint at a time. Try again after each one.

A solution

There’s always more than one right way. Read it, make sure you understand it, then try writing it yourself without looking.

class Stack {
  #items = [];
  push(item) {
    this.#items.push(item);
  }
  pop() {
    return this.#items.pop();
  }
  peek() {
    return this.#items.at(-1);
  }
  get size() {
    return this.#items.length;
  }
}

Learn what you need

This exercise uses what Sophomore Year: Classes & Object-Oriented JavaScript teaches. Read those notes first if any of it is new.