Updatify / React | Release notes

React

• Components can now render undefined: React no longer throws if you return undefined from a component. This makes the allowed component return values consistent with values that are allowed in the middle of a component tree. We suggest to use a linter to prevent mistakes like forgetting a return statement before JSX.
• In tests, act warnings are now opt-in: If you’re running end-to-end tests, the act warnings are unnecessary. We’ve introduced an opt-in mechanism so you can enable them only for unit tests where they are useful and beneficial.
• No warning about setState on unmounted components: Previously, React warned about memory leaks when you call setState on an unmounted component. This warning was added for subscriptions, but people primarily run into it in scenarios where setting state is fine, and workarounds make the code worse. We’ve removed this warning.
• No suppression of console logs: When you use Strict Mode, React renders each component twice to help you find unexpected side effects. In React 17, we’ve suppressed console logs for one of the two renders to make the logs easier to read. In response to community feedback about this being confusing, we’ve removed the suppression. Instead, if you have React DevTools installed, the second log’s renders will be displayed in grey, and there will be an option (off by default) to suppress them completely.
• Improved memory usage: React now cleans up more internal fields on unmount, making the impact from unfixed memory leaks that may exist in your application code less severe.

React DOM Server

• renderToString: Will no longer error when suspending on the server. Instead, it will emit the fallback HTML for the closest <Suspense> boundary and then retry rendering the same content on the client. It is still recommended that you switch to a streaming API like renderToPipeableStream or renderToReadableStream instead.
• renderToStaticMarkup: Will no longer error when suspending on the server. Instead, it will emit the fallback HTML for the closest <Suspense> boundary and retry rendering on the client.