Stacks and Queues

Stack

Follows a LIFO structure. Last In First Out. Last Element added to the stack is the first element to be removed.

Arrays can be used as a stack. provided LIFO is followed.
Linked lists can be used for stacks as only the order matters and other information like index etc that array provides are not needed.

Stack implementation
class Stack {
  constructor() {
    this.first = null;
    this.last = null;
    this.size = 0;
  }
}
class Node {
  constructor(value) {
    this.value = value;
    this.next = null;
  }
  push(val) {
    let newNode = new Node(val);
    if (!this.first) {
      this.first = newNode;
      this.last = newNode;
    } else {
      let temp = this.first;
      this.first = newNode;
      this.first.next = temp;
    }

    return ++this.size;
  }
  pop() {
    if (!this.first) {
      return undefined;
    }
    let temp = this.first;
    if (this.first === this.last) {
      this.last = null;
    }
    this.first = this.first.next;
    this.size--;
    return temp.value;
  }
}

Stack​

Stack