React

• Add Hooks — a way to use state and other React features without writing a class. (@acdlite et al. in #13968)
• Improve the useReducer Hook lazy initialization API. (@acdlite in #14723)

React DOM

• Bail out of rendering on identical values for useState and useReducer Hooks. (@acdlite in #14569)
• Use Object.is algorithm for comparing useState and useReducer values. (@Jessidhia in #14752)
• Don’t compare the first argument passed to useEffect/useMemo/useCallback Hooks. (@acdlite in #14594)
• Support synchronous thenables passed to React.lazy(). (@gaearon in #14626)
• Render components with Hooks twice in Strict Mode (DEV-only) to match class behavior. (@gaearon in #14654)
• Warn about mismatching Hook order in development. (@threepointone in #14585 and @acdlite in #14591)
• Effect clean-up functions must return either undefined or a function. All other values, including null, are not allowed. @acdlite in #14119

React Test Renderer and Test Utils

• Support Hooks in the shallow renderer. (@trueadm in #14567)
• Fix wrong state in shouldComponentUpdate in the presence of getDerivedStateFromProps for Shallow Renderer. (@chenesan in #14613)
• Add ReactTestRenderer.act() and ReactTestUtils.act() for batching updates so that tests more closely match real behavior. (@threepointone in #14744)

ESLint Plugin: React Hooks

• Initial release. (@calebmer in #13968)
• Fix reporting after encountering a loop. (@calebmer and @Yurickh in #14661)
• Don't consider throwing to be a rule violation. (@sophiebits in #14040)

Artifacts

• react: https://unpkg.com/react@16.8.0/umd/
• react-art: https://unpkg.com/react-art@16.8.0/umd/
• react-dom: https://unpkg.com/react-dom@16.8.0/umd/
• react-is: https://unpkg.com/react-is@16.8.0/umd/
• react-test-renderer: https://unpkg.com/react-test-renderer@16.8.0/umd/
• scheduler: https://unpkg.com/scheduler@0.13.0/umd/