There are auxiliary methods like top(), or sometimes called peek(), which are built-in functions that give you the value of what's on top of the stack. Here the top() function calls top.data which refers to the value inside of a node.
In the isEmpty() method, top is being compared to null. This is being done to check whether there is a value in the stack, or the stack is empty.
Attached is the full implementation of a stack using a linked list under the hood.
xxxxxxxxxx57
stack.printStack(); // Should print 2, 1class Node { constructor(value) { this.value = value; this.next = null; }}​class Stack { constructor() { this.top = null; }​ isEmpty() { return this.top === null; }​ push(value) { const newNode = new Node(value); newNode.next = this.top; this.top = newNode; }​ pop() { if (this.isEmpty()) { return null; } const removedNode = this.top; this.top = this.top.next; return removedNode.value;OUTPUT
:001 > Cmd/Ctrl-Enter to run, Cmd/Ctrl-/ to comment
