const stackA = new Stack();
  stackA.push("abc");
  stackA.push("xyz");
  console.log(stackA.stack);
  stackA.stack = [];
  console.log(stackA.stack);

  const stackB = createStack() 
  stackB.push("abc");
  stackB.push("xyz");
  console.log(stackB.stack);
  stackB.stack = [];
  console.log(stackB.stack);
  console.log(stackB.pop());

  const stackC = createStack() 
  console.log(stackC.pop());