DSA using JavaScript

Stack

// Define a Node for our linked list
function Node(value) {
    this.value = value;  // Store the value
    this.next = null;    // Pointer to the next node
}

// Define the Stack using linked list structure
function Stack() {
    this.top = null;  // Initialize the top of the stack as null
    this.size = 0;    // Track the size of the stack

    // Push: Add an item to the top of the stack
    this.push = function(value) {
        const newNode = new Node(value); // Create a new node
        newNode.next = this.top;         // Point the new node to the current top
        this.top = newNode;              // Update the top to the new node
        this.size++;                     // Increase the stack size
    };

    // Pop: Remove and return the item at the top of the stack
    this.pop = function() {
        if (this.isEmpty()) {
            return "Stack is empty";     // Return a message if the stack is empty
        }
        const topValue = this.top.value; // Store the top value to return
        this.top = this.top.next;        // Move the top pointer to the next node
        this.size--;                     // Decrease the stack size
        return topValue;                 // Return the popped value
    };

    // Peek: Return the top item without removing it
    this.peek = function() {
        if (this.isEmpty()) {
            return "Stack is empty";     // Return a message if the stack is empty
        }
        return this.top.value;           // Return the value of the top item
    };

    // isEmpty: Check if the stack has any items
    this.isEmpty = function() {
        return this.size === 0;          // Returns true if size is 0
    };

    // Size: Return the number of items in the stack
    this.getSize = function() {
        return this.size;                // Return the size of the stack
    };

    // Clear: Remove all items from the stack
    this.clear = function() {
        this.top = null;                 // Reset top to null
        this.size = 0;                   // Reset size to 0
    };
}

const stack = new Stack();

// Push items onto the stack
stack.push(10);
stack.push(20);
stack.push(30);

// Demonstrate each operation
console.log(stack.pop());       // Output: 30 (removes the top item)
console.log(stack.peek());      // Output: 20 (shows the current top)
console.log(stack.isEmpty());   // Output: false (stack is not empty)
console.log(stack.getSize());   // Output: 2 (two items left in the stack)
stack.clear();                  // Clear the stack
console.log(stack.isEmpty());   // Output: true (stack is now empty)