Lesson 1

Stacks in JavaScript: Understanding and Implementing Fundamental Data Structures

Topic Overview and Actualization

Hello, eager learners! In today's lesson, we're exploring Stacks, a crucial data structure in programming. We aim to understand Stacks, implement and manipulate Stacks in JavaScript, and analyze their complexities. Let's dive right in!

Introduction to Stacks

First and foremost, let's understand what a Stack is. Imagine a stack of plates that you can only remove from the top. This concept exemplifies Stacks, which follow a Last-In, First-Out (LIFO) structure. Let's see an implementation in JavaScript, where we'll Push (add), Pop (remove), and Peek (view the top) elements.

1class Stack { 2 constructor() {this.items = [];} // Empty Stack 3 isEmpty() {return this.items.length == 0;} // Check if Stack is empty 4}

We start with introducing the stack class that stores an array of items.

In JavaScript, arrays can work as Stacks. They have the necessary built-in methods. However, let's implement each operation ourselves to understand this data structure better.

Stack Operations — Push

The Push operation adds a new element to the top of the Stack. It is simply written as:

1push(element) { 2 this.items.push(element); 3}
Stack Operations — Pop

The Pop operation removes the topmost element from the Stack. It first checks if the Stack is empty, then returns "Underflow". Otherwise, it removes and returns the top element of the Stack.

1pop() { 2 return this.items.length == 0 ? "Underflow" : this.items.pop(); 3}
Stack Operations — Peek

The Peek operation lets us view the topmost element without removing it.

1peek() { 2 return this.items[this.items.length - 1]; 3}
Stack Complexity Analysis

The Push, Pop, and Peek operations take constant time — O(1). This is because these operations are performed at the end of the array. The space complexity is proportional to the number of elements — O(n), where n is the quantity of Stack elements.

Using Stack

Here is a complete stack implementation with usage example:

1class Stack { 2 constructor() {this.items = [];} // Empty Stack 3 4 push(element) { 5 this.items.push(element); 6 } // Add element 7 8 pop() { 9 return this.items.length == 0 ? "Underflow" : this.items.pop(); 10 } // Remove element 11 12 peek() { 13 return this.items[this.items.length - 1]; 14 } // Check top element 15 16 isEmpty() { 17 return this.items.length == 0; 18 } // Check if Stack is empty 19} 20 21let stack = new Stack(); 22stack.push(1); 23stack.push(2); 24stack.push(3); 25console.log(stack.pop()); // 3 26console.log(stack.peek()); // 2
Stacks in JavaScript

However, in JavaScript we usually don't implement stacks ourselves or use any special object for it. Instead, we simply use arrays as stacks:

1let stack = []; 2stack.push(1); 3stack.push(2); 4stack.push(3); 5console.log(stack.pop()); // 3 6console.log(stack[stack.length - 1]); // 2
Lesson Summary and Practice Announcement

Well done! You've completed your journey through Stacks in JavaScript, mastering their concept, implementation, operations, and complexity analysis. Exercise sessions await you to strengthen your skills further. So, let's set sail for some exciting hands-on practice!

Enjoy this lesson? Now it's time to practice with Cosmo!

Practice is how you turn knowledge into actual skills.