React JS Basics: What You Need to Know

React.js is a powerful JavaScript library for building user interfaces, especially for single-page applications. Created by Meta (formerly Facebook), React has become one of the most widely used tools for modern front-end development.

This post will guide you through the core concepts of React JS—without diving into code—so you can understand how it works and why it’s worth learning.

What is React?

React is a component-based library for creating fast, interactive UIs. Rather than updating the entire page when something changes, React only updates the parts of the DOM that need to change. This makes apps more efficient and responsive.

At its core, React lets you build encapsulated components that manage their own logic and UI, then combine them to create complex interfaces.

Core Concepts

1. Components

Think of components as the building blocks of a React application. Each component represents a part of the UI—like a button, form, or entire section of a page. Components can be reused and nested inside other components, which makes your code more modular and maintainable.

2. JSX

JSX stands for JavaScript XML. It allows you to write HTML-like syntax directly inside your JavaScript files. This makes it easier to visualize what the UI will look like. While it looks like HTML, JSX is compiled into JavaScript under the hood.

3. Props

Props (short for properties) are how components receive data from their parent. They are read-only and help pass information between components. This concept encourages a unidirectional data flow, which keeps the application predictable and easier to debug.

4. State

State refers to dynamic data that can change over time. Each component can have its own state, and when the state changes, React re-renders the component. This is how interactive features like counters, input forms, or toggle buttons work.

5. Hooks

Hooks are special functions introduced in newer versions of React that let you manage state and side effects in functional components. The most common hooks include:

• useState – for managing local state
• useEffect – for handling side effects like API calls
• useContext – for accessing shared state globally

6. Virtual DOM

React uses a Virtual DOM—a lightweight copy of the actual DOM. When something changes, React compares the new Virtual DOM with the old one and updates only the parts that have changed. This process is called reconciliation, and it's what makes React so fast.

Typical Project Structure

React applications often follow a clean folder structure to keep things organized:

• Public: Contains the HTML file
• Src: Contains JavaScript, CSS, and React components
• Components: A subfolder in src for reusable parts of the UI

This structure encourages separation of concerns and easier maintenance.

Why Use React?

• Efficiency: Updates the UI quickly with the Virtual DOM
• Modularity: Breaks the UI into independent, reusable pieces
• Scalability: Well-suited for both small widgets and large-scale applications
• Community: Large ecosystem and support, with libraries like React Router, Redux, and more

Summary

React JS simplifies UI development through a component-based architecture, a declarative approach, and a focus on performance. If you're learning front-end development, React is a great place to start due to its flexibility, popularity, and strong community.

Key Takeaways:

• React builds UI using components.
• JSX is a syntax that blends JavaScript and HTML.
• Props pass data; state handles change.
• Hooks allow functional components to manage logic.
• Virtual DOM makes updates fast and efficient.