Support index.jsx entry file

While I understand that the jsx extension is supported but not recommended, I was surprised that my index.jsx file isn’t being recognized after renaming it to pass eslint-config-airbnb’s jsx extension requirement.

Is this a bug report?

Sort of, I was surprised this wasn’t supported but it may be an intentionally missing feature.

Which terms did you search for in User Guide?

index.js, it’s clear that it’s currently expected for the filename to be an exact match.

Steps to Reproduce

1. Rename index.js to index.jsx
2. npm start

Expected Behavior

App runs normally, treating index.jsx as the same as index.js when it’s not present.

Actual Behavior

> react-scripts start

Could not find a required file.
  Name: index.js
  Searched in: /Users/nick/Repos/password-entropy/src
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! @ start: `react-scripts start`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the @ start script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

[nickmccurdy]

@torabian This may be simple for just create-react-app alone, but it doesn’t play well with developer tools. It took me at least an hour or two to get this working properly, and this affects a lot of people.

Here’s what this change involves for me:

1. Configure all Emacs modes to find JSX syntax in JS extension files. This is usually as simple as updating auto-mode-alist, but for packages like web-mode that handle multiple syntaxes, this quickly becomes complicated and difficult to debug.
2. Configure linter to allow JSX in JS files. I use eslint-config-airbnb, so I either have to violate its requirement or configure the rule to be disabled for this file. Either way, I should not need to violate linter or style guide rules because of technology choices.
3. If a project has any style guide documentation, you would have to document that index.jsx isn’t allowed and index.js has to be used instead, causing potential confusion and additional style guide violations.

[nickmccurdy]

That’s a great workaround, but I’m concerned about it creating confusion for contributors. If I haven’t used create-react-app before and I only had experience with React and Webpack, I wouldn’t be sure if I should be opening index.js or index.jsx to change functionality, and it wouldn’t be clear at first glance why both need to exist.