New Release

As with any major release, there are typically breaking changes. Although the changelog for React states "No New Features" there are a few. The TLDR for this is a preparation for the next version to resolve any issues they foresee in migration to the next major version. I'm going to highlight some changes with React and Create React App that will clean up code and increase some efficiency

JSX transform

Plenty of posts have already summarized this so I'm not gonna spend too much time on this. TLDR:

Fast Refresh

react-refresh is the successor for react-hot-loader. For some time, hot loading in react has been a great developer experience where we can keep our frontend application running and it will refresh when the changes are detected. What react-refresh does is a step further. If you are someone who builds client-side rendered applications and pass around a lot of state management in tools such as react context, redux, apollo, or really any react hooks, changes to your code no longer do a complete page refresh! It stores many of those changes and updates only the changes being made. My coworkers and I will love this because we have quite a bit of complex state management being passed around so we no longer lose our place when we want to make a minor JSX change! Here's a preview

Notice the changes to the return JSX and the imports and it still stores state. Get excited! I am!

Migrating an unejected Create React App project

Install updated packages

npm install react-scripts@4.0.0 react@17.0.0 react-dom@17.0.0

Remove old installation and version lock file

rm -rf node_modules package-lock.json

Although this isn't necessary if you run into any odd eslint related errors I found doing a clean install removed quite a few for me

Reinstall

npm install

Rebuild

npm run build

This is really only applicable to typescript projects. There is a flag that you'll see get set and after that...

Restart your app

npm run start

Potential issues others are running in to

Since create-react-app updated their eslint setup you may see some errors thrown that are new. I just spent the time to understand them and resolve them as I see fit. Some of the rules such as import order we're incorrect because I was using a relative import plugin. If you run into any other problems look for an existing issue or create your own here

Other issues

If you find an issue that hasn't been captured by the Facebook Create-react-app team here be a good open-source developer and create an issue. I had one where I was referencing an image under my public/ directory in a sass file to use as a background-image:... reference when myself and others realized the public directory is no longer available. Read more on this issue here

Migrating other projects

For most cases, you still would install the updates

npm install react@17.0.0 react-dom@17.0.0

After that, you would look up your specific platform. Both webpack and babel have plugins to help with the fast refresh and JSX transform config. If you're using other setup's such as react-app-rewired or NextJS refer to their documentation to lookup how others are migrating. It's less common so I am not going to be able to stay up-to-date with the latest way to migrate.