# JavaScript Data Structures: Stack: Recap

30 December 2019

## Intro

Last time, we added the last method.

I hope you learned something about the concept of a Stack and tried your best to implement it on your own.

### Thoughts about the Stack

We implemented the Stack using a Singly Linked List.

The Stack data structure is a very important concept, because we use it all the time.

The fundamental difference to the Singly and Doubly Linked List is the fact, that we only add and remove a node to/from the top of the Stack, so we use the "Last In, First Out"-Principle.

Examples in real life are a stack of cards, a pile of dishes, a browser history.

- Access:
`O(N)`

- Search:
`O(N)`

- Insert:
`O(1)`

- Remove:
`O(1)`

## Final Implementation

Our Stack has these methods:

`push`

, to add a node to the top of the stack`pop`

, to remove the top node from the stack

```
class Node {
constructor(value) {
this.value = value;
this.next = null;
}
}
class Stack {
constructor() {
this.length = 0;
this.last = null;
}
push(value) {
const newNode = new Node(value);
if (!this.length) {
this.last = newNode;
} else {
newNode.next = this.last;
this.last = newNode;
}
this.length += 1;
return newNode;
}
pop() {
if (!this.length) {
return null;
} else {
const nodeToRemove = this.last;
this.last = nodeToRemove.next;
nodeToRemove.next = null;
this.length -= 1;
return nodeToRemove;
}
}
}
```