react.dev/content/blog/2018-10-01-create-react-app-v2.md

title	author
Create React App 2.0: Babel 7, Sass, and More	[timer gaearon]

Create React App 2.0 has been released today, and it brings a year's worth of improvements in a single dependency update.

While React itself doesn't require any build dependencies, it can be challenging to write a complex app without a fast test runner, a production minifier, and a modular codebase. Since the very first release, the goal of Create React App has been to help you focus on what matters the most -- your application code -- and to handle build and testing setup for you.

Many of the tools it relies on have since released new versions containing new features and performance improvements: Babel 7, webpack 4, and Jest 23. However, updating them manually and making them work well together takes a lot of effort. And this is exactly what Create React App 2.0 contributors have been busy with for the past few months: migrating the configuration and dependencies so that you don't need to do it yourself.

Now that Create React App 2.0 is out of beta, let's see what's new and how you can try it!

Note

Don't feel pressured to upgrade anything. If you're satisfied with the current feature set, its performance, and reliability, you can keep using the version you're currently at! It might also be a good idea to let the 2.0 release stabilize a little bit before switching to it in production.

What's New

Here's a short summary of what's new in this release:

• 🎉 More styling options: you can use Sass and CSS Modules out of the box.
• 🐠 We updated to Babel 7, including support for the React fragment syntax and many bugfixes.
• 📦 We updated to webpack 4, which automatically splits JS bundles more intelligently.
• 🃏 We updated to Jest 23, which includes an interactive mode for reviewing snapshots.
• 💄 We added PostCSS so you can use new CSS features in old browsers.
• 💎 You can use Apollo, Relay Modern, MDX, and other third-party Babel Macros transforms.
• 🌠 You can now import an SVG as a React component, and use it in JSX.
• 🐈 You can try the experimental Yarn Plug'n'Play mode that removes node_modules.
• 🕸 You can now plug your own proxy implementation in development to match your backend API.
• 🚀 You can now use packages written for latest Node versions without breaking the build.
• ✂️ You can now optionally get a smaller CSS bundle if you only plan to target modern browsers.
• 👷‍♀️ Service workers are now opt-in and are built using Google's Workbox.

All of these features work out of the box -- to enable them, follow the below instructions.

Starting a Project with Create React App 2.0

You don't need to update anything special. Starting from today, when you run create-react-app it will use the 2.0 version of the template by default. Have fun!

If you want to use the old 1.x template for some reason, you can do that by passing --scripts-version=react-scripts@1.x as an argument to create-react-app.

Updating a Project to Create React App 2.0

Upgrading a non-ejected project to Create React App 2.0 should usually be straightforward. Open package.json in the root of your project and find react-scripts there.

Then change its version to 2.0.3:

  // ... other dependencies ...
  "react-scripts": "2.0.3"

Run npm install (or yarn, if you use it). For many projects, this one-line change is sufficient to upgrade!

working here... thanks for all the new functionality 👍

— Stephen Haney (@sdothaney) October 1, 2018

Here are a few more tips to get you started.

When you run npm start for the first time after the upgrade, you'll get a prompt asking about which browsers you'd like to support. Press y to accept the default ones. They'll be written to your package.json and you can edit them any time. Create React App will use this information to produce smaller or polyfilled CSS bundles depending on whether you target modern browsers or older browsers.

If npm start still doesn't quite work for you after the upgrade, check out the more detailed migration instructions in the release notes. There are a few breaking changes in this release but the scope of them is limited, so they shouldn't take more than a few hours to sort out. Note that support for older browsers is now opt-in to reduce the polyfill size.

If you previously ejected but now want to upgrade, one common solution is to find the commits where you ejected (and any subsequent commits changing the configuration), revert them, upgrade, and later optionally eject again. It's also possible that the feature you ejected for (maybe Sass or CSS Modules?) is now supported out of the box.

Note

Due to a possible bug in npm, you might see warnings about unsatisfied peer dependencies. You should be able to ignore them. As far as we're aware, this issue isn't present with Yarn.

Breaking Changes

Here's a short list of breaking changes in this release:

• Node 6 is no longer supported.
• Support for older browsers (such as IE 9 to IE 11) is now opt-in with a separate package.
• Code-splitting with import() now behaves closer to specification, while require.ensure() is disabled.
• The default Jest environment now includes jsdom.
• Support for specifying an object as proxy setting was replaced with support for a custom proxy module.
• Support for .mjs extension was removed until the ecosystem around it stabilizes.
• PropTypes definitions are automatically stripped out of the production builds.

If either of these points affects you, 2.0.3 release notes contain more detailed instructions.

Learn More

You can find the full changelog in the release notes. This was a large release, and we may have missed something. Please report any problems to our issue tracker and we'll try to help.

Note

If you've been using 2.x alpha versions, we provide separate migration instructions for them.

Thanks

This release wouldn't be possible without our wonderful community of contributors. We'd like to thank Andreas Cederström, Clement Hoang, Brian Ng, Kent C. Dodds, Ade Viankakrisna Fadlil, Andrey Sitnik, Ro Savage, Fabiano Brito, Ian Sutherland, Pete Nykänen, Jeffrey Posnick, Jack Zhao, Tobias Koppers, Henry Zhu, Maël Nison, XiaoYan Li, Marko Trebizan, Marek Suscak, Mikhail Osher, and many others who provided feedback and testing for this release.