Some developers (including FB) are using .js for React JSX files now, instead of the .jsx extension. I think the best argument for this is that, while JSX features aren't in the ES2016/7 spec, they may be eventually. And when you're transpiling your code to JS in the end anyway (potentially using JSX, Flow, and other tools that aren't actually valid ES2016/7 code), it's simpler to call it .js than think about renaming files when you add more steps to your babel process (file.flow.jsx.xyz...).

It hasn't taken off completely, and personally I like having the ".jsx" extension indicate that file will export a React component instead of plain javascript.

There are lots of arguments online about this: https://github.com/facebook/react/issues/3582#issuecomment-8... https://www.reddit.com/r/reactjs/comments/4kkrwg/ask_js_or_j...