16.3: Introduce aliases for the unsafe lifecycles, UNSAFE_componentWillMount, UNSAFE_componentWillReceiveProps, and UNSAFE_componentWillUpdate. (Both the old lifecycle names and the new aliases will work in this release.)
A future 16.x release: Enable deprecation warning for componentWillMount, componentWillReceiveProps, and componentWillUpdate. (Both the old lifecycle names and the new aliases will work in this release, but the old names will log a DEV-mode warning.)
17.0: Remove componentWillMount, componentWillReceiveProps, and componentWillUpdate . (Only the new “UNSAFE_” lifecycle names will work from this point forward.)