React is one of the most popular JavaScript libraries for building user interfaces.
In this lesson, you will learn what React is, why it exists, and what problems it solves compared to traditional JavaScript development.
What Is React?
React is an open-source JavaScript library created by Facebook for building user interfaces.
It focuses on the view layer of an application and allows developers to build reusable UI components.
Key characteristics of React:
- Component-based architecture
- Declarative UI
- Efficient rendering using Virtual DOM
- Strong ecosystem and community
React does not replace JavaScript — it extends it.
Why Was React Created?
Before React, developers manipulated the DOM directly using JavaScript or libraries like jQuery.
As applications grew larger, this approach caused problems:
- Complex and hard-to-maintain code
- Manual DOM updates
- Poor performance
- Difficult state management
React was created to solve these issues by introducing a component-driven and state-based model.
Single Page Applications (SPA)
React is commonly used to build Single Page Applications.
In a SPA:
- The page loads once
- JavaScript updates the UI dynamically
- No full page reloads
- Faster and smoother user experience
React updates only the parts of the page that change instead of reloading everything.
Declarative vs Imperative Code
Imperative approach (Vanilla JS)
You tell the browser how to update the UI step by step.
Declarative approach (React)
You describe what the UI should look like based on the current state.
React handles the DOM updates automatically when the state changes.
This makes code:
- Easier to read
- Easier to debug
- Easier to scale
Component-Based Architecture
In React, everything is built using components.
A component:
- Is a reusable piece of UI
- Has its own logic and structure
- Can receive data (props)
- Can manage its own state
Examples of components:
- Button
- Header
- ProductCard
- Navbar
Large applications are built by combining many small components.
Virtual DOM Explained
React uses a Virtual DOM to improve performance.
How it works:
- React creates a virtual representation of the UI
- When state changes, React compares the new Virtual DOM with the old one
- Only the differences are applied to the real DOM
This process is called diffing and makes UI updates fast and efficient.
When Should You Use React?
React is a great choice when:
- Your UI is complex and dynamic
- You need reusable components
- Your app has many user interactions
- You want long-term maintainability
React may be unnecessary for very small or static websites.
Summary
In this lesson, you learned:
- What React is
- Why React was created
- What problems it solves
- What a Single Page Application is
- The difference between imperative and declarative code
- The basics of component-based architecture
- How the Virtual DOM works
In the next lesson, we will set up the React development environment and create your first React project.