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Intermediate Topic 27 of 51 Web Development

React Fundamentals

Component-based UI library using a virtual DOM.

How it works

React is a JavaScript library for building user interfaces from components, functions that take props and return a description of the UI in JSX. State, managed with hooks such as useState and useReducer, triggers re-rendering when it changes, and React updates the DOM efficiently by diffing a virtual representation. useEffect runs side effects after rendering, and context shares values without prop drilling. Data flows one way, from parent to child.

Step-by-step walkthrough

  1. UI is built from components, functions returning markup.
  2. State or props change.
  3. The component re-renders into a new virtual tree.
  4. React diffs it against the previous one.
  5. Only the changed DOM nodes are updated.

Where it is used

Web applications, mobile apps with React Native, design systems and server-rendered sites with frameworks such as Next.js use React.

Common pitfall

Mutating state directly instead of using setters prevents updates. Missing or wrong dependency arrays in useEffect cause stale values or infinite loops. Using array index as key in lists breaks identity when order changes. Heavy renders need memoization and splitting. Keep components small and pure, derive values instead of duplicating state and lift state only as needed.

Where it fits in the course

React Fundamentals is topic 27 of 51 in Web Development, rated Intermediate. It follows Single Page Applications. The next topic is State Management.

Practice and explore

How to study this topic

  1. Read the explanation above and restate the definition in your own words.
  2. Open the interactive lesson and answer its mini quiz.
  3. Read the common pitfall, then write a short example that avoids it.
  4. Check your understanding in the Web Development quiz, and revisit the topic if you miss a question.

Frequently asked questions

What is React Fundamentals?
Component-based UI library using a virtual DOM. It belongs to Web Development and is an intermediate-level topic.
Where do people use React Fundamentals?
Web applications, mobile apps with React Native, design systems and server-rendered sites with frameworks such as Next.js use React.
What is the most common mistake with React Fundamentals?
Mutating state directly instead of using setters prevents updates.
What should I learn before this topic?
Start with Single Page Applications, the topic just before it in Web Development.
How can I practice it?
Answer the mini quiz in the interactive lesson, then take the Web Development quiz.
Is React Fundamentals hard to learn?
It is an Intermediate topic. Be comfortable with the Beginner topics in this area first, then read the common pitfall carefully, since it is where most mistakes happen.
How long does it take to learn React Fundamentals?
Most learners can read the explanation and finish the interactive lesson in under an hour. Fluency comes from applying the idea, so plan a few short practice sessions with the quiz.
Which topics are related to React Fundamentals?
Single Page Applications, State Management, ARIA are closely connected. The full list is in the related topics section of this page.
What should I study after React Fundamentals?
Continue with State Management, the next topic in Web Development.

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