dumbStack.js

function makeStack() {
  let head = null
  function push(item) {
    if (head == null) head = { value: item }
    else head = { value: item, next: head }
  }
  function isEmpty() {
    return head == null
  }
  function peek() {
    return head ? head.value : null
  }
  function pop() {
    const value = head ? head.value : null
    if (value) head = head.next
    return value
  }
  return { isEmpty, push, peek, pop }
}