Stack Data Structure Example

stack.js

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

class Stack {
    constructor() {
        this.first = null;
        this.last = null;
        this.size = 0;

    }
    push(value) {
        const newNode = new Node(value);

        if (this.first) {

            newNode.next = this.first;
            this.first = newNode;

        } else {
            this.first = newNode;
            this.last = newNode;
        }

        this.size++;

        return this.size;
    }
    pop() {
        if (!this.size) return null;

        const removedNode = this.first;
        if (this.first == this.last) {
            this.last = null;
        }

        this.first = removedNode.next;
        this.size--;

        return removedNode.value;
    }
}

Another solution

class Stack {
  constructor() {
    this.items = [];
  }

  push(value) {
    this.items.push(value);
    return this.items.length;
  }

  pop() {
    return this.items.pop() ?? null;
  }

  peek() {
    return this.items[this.items.length - 1] ?? null;
  }

  isEmpty() {
    return this.items.length === 0;
  }

  length() {
    return this.items.length;
  }
}