Create React App v4.0.0 Has Released

Create React App v4.0.0 release a major update with several new features, including support for Fast Refresh!
The New Version Includes New Features and supports are list below:

Create React App v4 Highlights

• Fast Refresh
• React 17 support includes the new JSX transform
• TypeScript 4 support
• New ESLint 7 Rules : New Jest and React Testing Library rules
• Jest 26
• PWA/workbox improvements
  1: Switch to the Workbox InjectManifest plugin
  2: Now its own template so it can be released independently
• Web Vitals support

Migrating from 3.4.x to 4.0.0

You can update the react version Inside any created project that has not been ejected, run:

npm install --save --save-exact react-[email protected]

OR

yarn add --exact [email protected]

Note:
you may have to delete your node_modules folder and reinstall your dependencies by running yarn (or npm install) if you encounter errors after upgrading.

Breaking Changes

[email protected] contains a number of breaking changes. We expect that they won’t affect every user, but they recommend us to look over this section to see if something is relevant to you. If we missed something, you can file a new issue over repository.

ESLint

It has upgraded to ESLint 7 and added many new rules including some for Jest and React Testing Library as well as the import/no-anonymous-default-export rule. It has also upgraded eslint-plugin-hooks to version 4.0.0 and removed the EXTEND_ESLINT flag as it is no longer required to customize the ESLint config.

Jest

It has upgraded to Jest 26 and now set resetMocks to true by default in the Jest config.

Service workers

It has switched to the Workbox InjectManifest plugin and moved the PWA templates into their own repository.

Removed typescript flag and NODE_PATH support

It has removed the deprecated typescript flag when creating a new app. Use --template typescript instead. It also dropped deprecated NODE_PATH flag as this has been replaced by setting the base path in jsconfig.json.

Dropped Node 8 support

Node 8 reached End-of-Life at the end of 2019 and is no longer supported.

Fix dotenv file loading order

It has changed the loading order of env files to match the dotenv specification.

Links

Release Date: October 23, 2020
Detailed Change Log: Changelog in details
Change Log: Create React App 4.0.0