Implement a Stack in Javascript

Objective:

• Implement a class-based Stack data structure in JavaScript with standard stack operations.

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Requirements:

1. Create a Stack class that implements the following methods:
   • push(element) — Adds an element to the top of the stack.
   • pop() — Removes and returns the top element from the stack. Returns null if the stack is empty.
   • peek() — Returns the top element of the stack without removing it. Returns null if the stack is empty.
   • isEmpty() — Returns true if the stack is empty, otherwise returns false.
   • size() — Returns the number of elements in the stack.
2. The stack should use an internal array to store elements and follow LIFO order.

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Steps:

1. Define the Stack Class:

   • Use a class in JavaScript to define the stack.
   • Store the stack elements in an internal array.

2. Implement the Methods:

   • push(element) — Add the element to the top (end) of the array.
   • pop() — Remove and return the last element from the array (top of the stack). Handle the case where the stack is empty.
   • peek() — Return the last element from the array without removing it.
   • isEmpty() — Check if the length of the array is zero.
   • size() — Return the length of the internal array.

3. Test the Stack:

   • Create a stack instance and use the methods to ensure they behave as expected.
   • Test edge cases such as popping from an empty stack or peeking into an empty stack.

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Resources:

• Stack Data Structure
• JavaScript Classes
• Array Methods in JavaScript

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Solution:

Here’s the solution for the stack implementation in JavaScript:

// Stack class implementation
class Stack {
  constructor() {
    this.stack = [];  // Internal array to store stack elements
  }

  // Pushes an element onto the top of the stack
  push(element) {
    this.stack.push(element);
  }

  // Pops the top element from the stack and returns it
  pop() {
    if (this.isEmpty()) {
      return null; // Return null if the stack is empty
    }
    return this.stack.pop(); // Remove and return the top element
  }

  // Returns the top element of the stack without removing it
  peek() {
    if (this.isEmpty()) {
      return null; // Return null if the stack is empty
    }
    return this.stack[this.stack.length - 1]; // Return the last element
  }

  // Checks if the stack is empty
  isEmpty() {
    return this.stack.length === 0; // True if no elements in the stack
  }

  // Returns the size of the stack
  size() {
    return this.stack.length;
  }
}

// Example Usage
const myStack = new Stack();

myStack.push(10);
myStack.push(20);
myStack.push(30);

console.log(myStack.peek());  // Output: 30
console.log(myStack.pop());   // Output: 30
console.log(myStack.size());  // Output: 2
console.log(myStack.isEmpty()); // Output: false
myStack.pop();
myStack.pop();
console.log(myStack.isEmpty()); // Output: true