React 17 attaches events to the root DOM container instead of the document node

React 17 delegates events to the root node instead of the document node, making it easier to embed React into apps built with other technologies

React 17 introduces new JSX transform

React 17 introduces jsx-runtime and jsx-dev-runtime that enables the user to write JSX without importing React.

React 17 internally uses the browser's focusin and focusout events for onFocus and onBlur events

React's onFocus and onBlur events have switched to using the native focusin and focusout events under the hood.