ReactJS - .JS vs .JSX

There is none when it comes to file extensions. Your bundler/transpiler/whatever takes care of resolving what type of file contents there is.

There are however some other considerations when deciding what to put into a .js or a .jsx file type. Since JSX isn't standard JavaScript one could argue that anything that is not "plain" JavaScript should go into its own extensions ie., .jsx for JSX and .ts for TypeScript for example.

There's a good discussion here available for read

In most of the cases it’s only a need for the transpiler/bundler, which might not be configured to work with JSX files, but with JS! So you are forced to use JS files instead of JSX.

And since react is just a library for javascript, it makes no difference for you to choose between JSX or JS. They’re completely interchangeable!

In some cases users/developers might also choose JSX over JS, because of code highlighting, but the most of the newer editors are also viewing the react syntax correctly in JS files.

JSX tags (<Component/>) are clearly not standard javascript and have no special meaning if you put them inside a naked <script> tag for example. Hence all React files that contain them are JSX and not JS.

By convention, the entry point of a React application is usually .js instead of .jsx even though it contains React components. It could as well be .jsx. Any other JSX files usually have the .jsx extension.

In any case, the reason there is ambiguity is because ultimately the extension does not matter much since the transpiler happily munches any kinds of files as long as they are actually JSX.

My advice would be: don't worry about it.