React .js vs .jsx: Differences, Usage & Best Practices

In React, both .js and .jsx files fully support JSX syntax since tools like Babel transpile it no matter the extension. The key difference? .jsx acts as a visual cue for React components packed with JSX elements, improving code navigation and editor smarts. Stick to .jsx for anything rendering UI, and reserve .js for plain logic like hooks or utils—it’s a convention that scales projects nicely.

Contents

• What Are .js and .jsx Files in React?
• Can JSX Syntax Be Used in Both .js and .jsx Files?
• Key Differences Between .js and .jsx Extensions
• When to Prefer .jsx Over .js in React Projects
• Tooling and Editor Support: ESLint, Emmet, and Bundlers
• Best Practices and React Official Guidance
• Sources
• Conclusion

What Are .js and .jsx Files in React?

Think of .js files as your standard JavaScript workhorses. They’ve been around forever, handling everything from loops to API calls without batting an eye. In React? They’re perfect for non-UI stuff—say, a custom hook that fetches data or a utility function crunching numbers.

.jsx flips the script. That “x” stands for XML-ish syntax, nodding to JSX’s blend of JavaScript and HTML-like tags. It’s not a new language; just sugar for React.createElement() calls under the hood. When you see App.jsx, you instantly know: this bad boy’s rendering DOM elements.

But here’s the kicker—React doesn’t care about the extension at runtime. Browsers chug vanilla JS anyway. The magic happens during build, courtesy of Babel or esbuild. Still, naming matters in team workflows. Ever scanned a folder with 50 files and wondered which ones spit out JSX? .jsx solves that glance-test.

Can JSX Syntax Be Used in Both .js and .jsx Files?

Short answer: yes, absolutely. Drop <div>Hello, React!</div> into a .js file, and as long as your bundler (Webpack, Vite, whatever) runs Babel, it’ll compile fine. No errors, no fuss.

Why does this work? JSX isn’t native JS—it’s a preprocessor step. Babel’s @babel/preset-react plugin sniffs for JSX regardless of filename. Config your babel.config.json like this:

{
 "presets": ["@babel/preset-react"]
}

And boom—JSX in .js flies. Same for TypeScript with .ts or .tsx. Developers on Stack Overflow confirm: functionality matches 1:1.

That said, mixing them can trip up newbies. Imagine linting yelling about unescaped JSX in .js. Or your IDE not auto-completing className. It works, but why fight the friction?

Key Differences Between .js and .jsx Extensions

Functionally? Zilch. Both transpile to identical JS. But practically, they diverge big time.

.jsx screams “UI component ahead,” which shines in monorepos. .js keeps things vanilla for shared libs. One dev noted in discussions: without .jsx, “it’s like hiding puzzles in plain sight—functional, but annoying.”

Performance? Negligible. Bundle size stays the same. It’s all about DX (developer experience).

When to Prefer .jsx Over .js in React Projects

Reach for .jsx whenever JSX touches the file. Rendering a list? List.jsx. Form with props? Form.jsx. Even entry points like index.jsx if they’re component-heavy.

Save .js for:

• Reducers or selectors (Redux vibes).
• API wrappers.
• Tests without snapshots.

Why? Scale. In a 100+ component app, .jsx files cluster nicely in VS Code’s explorer. Search “jsx” and bam—UI layer exposed.

Consider container/presentational split: logic in UserContainer.js, markup in UserView.jsx. Clean separation. For SPAs, App.jsx as root makes sense too.

But solo projects? .js everywhere works if consistent. Just don’t flip-flop—pick a rule, enforce via ESLint.

What about Next.js or Remix? They lean .jsx for pages/components, .js for utils. Matches the React jsx js crowd’s habits.

Tooling and Editor Support: ESLint, Emmet, and Bundlers

This is where .jsx pulls ahead. ESLint’s react/jsx-filename-extension rule defaults to whining about JSX in .js:

// .eslintrc.json
{
 "rules": {
 "react/jsx-filename-extension": [1, { "extensions": [".jsx", ".tsx"] }]
 }
}

Tweak it, sure—but why? .jsx avoids the hassle.

Emmet in VS Code? Type div.btn in .jsx, get <div className="btn"></div>. In .js? Sticks to class. Game-changer for rapid prototyping.

Bundlers like Vite auto-handle both via vite-plugin-react. But .jsx gets explicit love in docs: better tree-shaking hints.

Icons in IDEs? .jsx often sports React logos. Tiny win, but folders light up.

Stack Overflow threads hammer this: “Emmet alone justifies .jsx,” says one engineer. ESLint jsx catches more eyes too.

Best Practices and React Official Guidance

React docs don’t mandate .jsx—check react.dev—but they demo it heavily for components. Legacy site echoes: “Use .jsx for clarity.”

Airbnb style guide? .jsx only for JSX files. Prettier formats both fine.

Rules of thumb:

1. JSX present → .jsx.
2. Team > personal pref—docs it.
3. TypeScript? .tsx mirror.
4. Monorepo? Consistent across packages.

Edge case: SSR with Node.js? .jsx still rules, as transpilation’s server-side too.

In practice, giants like Facebook (React’s home) mix but favor .jsx for components. Why fight winning patterns?

Sources

1. Stack Overflow: .js vs .jsx in React — Comprehensive Q&A on functional differences and conventions: https://stackoverflow.com/questions/46169472/what-is-the-difference-between-using-js-vs-jsx-files-in-react
2. React Official Documentation — Guides on JSX syntax and component structure: https://react.dev/learn/writing-markup-with-jsx
3. React Legacy Docs — Historical context on JSX transpilation and extensions: https://legacy.reactjs.org/docs/jsx-in-depth.html
4. GeeksforGeeks: React File Extensions — Tutorial covering .js vs .jsx use cases: https://www.geeksforgeeks.org/difference-between-js-and-jsx-file/

Conclusion

Bottom line: JSX runs in both .js and .jsx, but .jsx wins for React projects by boosting clarity, tooling, and team flow. Use it for components, .js for everything else—your future self (and coworkers) will thank you. Consistency trumps perfection; align with your stack’s norms and watch productivity climb.