React version 17 will deprecate several of the class component API lifecycles: componentWillMount, componentWillReceiveProps, and componentWillUpdate. A couple of new lifecycles are also being added to better support async rendering mode.

Typically, this type of change would require third party libraries to release a new major version in order to adhere to semver. However, the react-lifecycles-compat polyfill offers a way to use the new lifecycles with older versions of React as well (0.14.9+) so no breaking release is required. This enables shared libraries to support both older and newer versions of React simultaneously.

Node.js is an event-based server-side JavaScript engine.