React

React is a JavaScript library, originally created at Facebook and now maintained by Meta and the community, for building user interfaces out of components. You describe what the UI should look like for a given state, and React updates the DOM to match.

Why it matters

React is one of the most widely used front-end technologies, so its ecosystem, hiring pool and tooling are large. It is often paired with a meta-framework for routing and server rendering. For site owners, the practical effects are bundle size, build requirements and the need for hydration when pages are rendered on the server.

Example

function Welcome({ name }) {
  return <h1>Hello, {name}</h1>;
}
// <Welcome name="Dev" /> renders: Hello, Dev

The JSX syntax looks like HTML but is compiled by a transpiler into JavaScript calls before the browser sees it.

Common mistakes

• Calling React a full framework. It does not include routing or data fetching by itself.
• Putting everything in one giant component instead of splitting by responsibility.
• Mutating state directly instead of using the setter, so the view does not update.

Related

• JavaScript Framework
• Hydration
• Transpiler
• Single-Page Application
• Tool: Page weight analyzer

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