Implementation of the stack data structure in JavaScript.

javascript-stack.js

class Item {
  // stores given value and points to nothing
  constructor (value) {
    this.value = value
    this.next = null
  }
}

class Stack {
  // initial size is 0 and initially just has a head node that stores nothing and points to nothing
  constructor () {
    this.size = 0
    this.top = new Item(null)
  }

  // helper function to test
  // prints all items in stack in console
  printItems = () => {
    let item = this.top

    if (item.next) {
      while (item.next !== null) {
        item = item.next
        console.log(item.value)
      }
    } else console.log('Stack empty')
  }

  push = value => {
    // create new node
    let item = new Item(value)

    // make new item point to current last item
    item.next = this.top.next

    // connect top to new iem
    this.top.next = item

    this.size++
  }

  pop = () => {
    // if no item, return
    if (this.top.next === null) {
      console.log("Stack empty.")
      return null
    }

    // assign last item to temp
    let temp = this.top.next

    // connect top to second to last item
    this.top.next = temp.next

    // disconnect previous last item from stack
    temp.next = null

    this.size--

    return temp.value
  }

  stackTop = () => {
    // if there's a top item
    if (this.top.next) {
      let firstItem = this.top.next
      return firstItem.value
    } else return null
  }

  isEmpty = () => {
    if (!this.top.next) return true
    else return false
  }

  stackSize = () => {
    return this.size
  }
}


// tests

// const stack = new Stack()
// stack.printItems()

// console.log('size', stack.stackSize())

// stack.push(7)
// stack.push(8)
// stack.push(5)
// stack.printItems()

// console.log('size', stack.stackSize())
// console.log('top', stack.stackTop())

// const removed = stack.pop()
// console.log('removed', removed)
// stack.printItems()

// console.log('empty', stack.isEmpty())

// stack.pop()

// stack.printItems()
// console.log('empty', stack.isEmpty())
// console.log('top', stack.stackTop())

// stack.pop()
// console.log('empty', stack.isEmpty())
// console.log('top', stack.stackTop())

// console.log('size', stack.stackSize())
// console.log('removed', stack.pop())