- you will now see a warning when using any of the old names of unsafe lifecycle method
- No support for “factory” component that returns an object with a render method
- act() testing utility also accepts asynchronous functions
- programmatic way to gather measurements called - measures how often app renders and what's the "cost" of render is
- A crash when calling findDOMNode() inside a tree has been fixed.
- A memory leak caused by retaining deleted subtrees has been fixed too.
- An infinite loop caused by setState in useEffect now logs an error. (This is similar to the error you see when you call setState in componentDidUpdate in a class.)