React Basics
React Introduction
React is a free, open-source JavaScript library created at Meta for building user interfaces out of small, reusable pieces called components. Instead of writing step-by-step DOM instructions, you describe what the screen should look like for a given state, and React works out the minimum set of DOM changes needed to get there.
What is Introduction in React?
React is a free, open-source JavaScript library created at Meta for building user interfaces out of small, reusable pieces called components. Instead of writing step-by-step DOM instructions, you describe what the screen should look like for a given state, and React works out the minimum set of DOM changes needed to get there.
Why Introduction matters
React powers a very large share of the front-end job market in India — most "React developer", "front-end intern" and "MERN stack" openings expect it. Because the same component model is reused by React Native, Next.js and Remix, learning React once unlocks web, mobile and full-stack roles.
Introduction example
function Welcome() {
return <h1>Hello, React!</h1>;
}
export default Welcome;How this works
A component is just a JavaScript function whose name starts with a capital letter and which returns markup. React calls that function, gets back a description of the UI, and renders it into the page. There is no template language to learn — the logic and the markup live together in ordinary JavaScript.
Key points to remember
- React is a library, not a full framework — routing and data fetching come from separate packages.
- It is declarative: you describe the result, not the DOM steps to reach it.
- The UI is composed from components, which can be nested and reused freely.
- Data flows one way — from parent down to child through props.
- React is maintained by Meta and a very large open-source community.
React compared with other front-end options
| React | Angular | Vue | |
|---|---|---|---|
| Type | Library (UI only) | Full framework | Progressive framework |
| Language | JavaScript / JSX | TypeScript first | JavaScript / TS |
| Learning curve | Gentle start, deep ecosystem | Steeper — DI, RxJS, modules | Gentlest |
| Built-in routing/HTTP | No — add packages | Yes | Official packages |
| Typical Indian job demand | Very high | High (enterprise, banking) | Moderate |
Common mistakes with Introduction
- Expecting React to include routing, forms or HTTP out of the box — it does not.
- Learning React before you are comfortable with JavaScript functions, arrays and destructuring.
- Copying class-component tutorials from 2018 — modern React is written with function components and hooks.
Before starting React, make sure you are comfortable with arrow functions, array map/filter, destructuring, spread syntax and ES modules. Those five features appear in almost every React file.
React Introduction— Interview Questions & FAQs
Is React a framework or a library?+
React is a library. It only handles the view layer — rendering components and keeping them in sync with state. Routing, HTTP calls, form validation and global state come from separate packages such as React Router, Axios and Redux Toolkit.
Do I need to know JavaScript before learning React?+
Yes. You should be comfortable with ES6 features — arrow functions, destructuring, spread/rest, template literals, array methods like map and filter, promises and async/await. Most "React is hard" complaints are really JavaScript gaps.
How long does it take to learn React?+
With 1–2 hours of daily practice, most learners reach a job-ready level of React in about 8–10 weeks: two weeks on components and props, three on hooks and state, and the rest on routing, data fetching and one real project.