React Introduction
Learn what React is, how it differs from traditional HTML and JavaScript development, and why it is the most popular frontend library.
Learning Goals
The Core Concept
React is an open-source JavaScript library created by Facebook in 2013 for building user interfaces. Instead of writing separate HTML pages and using complex JavaScript to manually update individual elements, React introduces a declarative, component-based approach.
With React, you break your interface down into small, reusable building blocks called Components. Each component handles its own design and logic. React updates only the specific parts of the screen that changed by using a fast Virtual DOM, rather than reloading the entire browser page. In this introduction, we'll look at the fundamental difference between 'old-school' Javascript DOM manipulation and the React way.
Visual guide
React concept flow
A simple original diagram to connect the lesson idea with real project flow.
Code & Implementation
// React component structure
// A React component is just a Javascript function that returns UI structure (JSX)
export default function App() {
return (
<div style={{ padding: '20px', fontFamily: 'sans-serif' }}>
<h1>Welcome to React!</h1>
<p>React is built around reusable components and declarative UI.</p>
</div>
);
}Expected Output
UI preview: - Heading: Welcome to React! - Text: React is built around reusable components...
Your First Custom Component
Hands-on practice task
The Challenge
Write a React component named WelcomeBanner that returns a section with a heading greeting visitors and a paragraph containing today's tip.
Helpful Hints
- •Define a function WelcomeBanner().
- •Return a single parent element (like a div or section) containing the heading and paragraph.
Quick Knowledge Check
Do I need to know JavaScript before learning React?
Why are React component names capitalized?
Continue Learning
Next steps after this lesson
Write a React component named WelcomeBanner that returns a section with a heading greeting visitors and a paragraph containing today's tip.
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