SOURCE

// push methods
function append(e) {
  this.stackList.push(e)
}

// pop methods
function pop() {
  this.stackList.pop()
}

// peek methods
function peek() {
  return this.stackList[this.size() - 1]
}

// isEmpty methods
function isEmpty() {
  return !this.stackList.length
}

// clear methods
function clear() {
  this.stackList = []
}

// size methods
function size() {
  return this.stackList.length;
}

// Stack structure
function Stack() {
  this.stackList = [];
  this.append = append;
  this.pop = pop;
  this.peek = peek;
  this.isEmpty = isEmpty;
  this.clear = clear;
  this.size = size;
}

let stack = new Stack()

stack.append('1')
stack.append('2')
stack.append('2')


console.log(stack.size())
console.log(stack.peek())