stack.js

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

  get() {
    return this.stack;
  }

  pop() {
    return this.stack.pop();
  }

  push(num) {
    return this.stack.push(num);
  }
}

function main() {
  const stack = new Stack([1, 2, 3]);

  stack.pop();
  stack.push(4);
  return stack.get();
}

console.log(main());