React Tldr; React v16.9.0

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New Deprecations:

  • you will now see a warning when using any of the old names of unsafe lifecycle method
  • Using "javascript:" URLs now will log a warning
  • No support for β€œfactory” component that returns an object with a render method

New Features:

  • 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.)


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Building the most demanding and challenging interfaces with React.