A function provides the simplest way to interact with the component rendering engine. The functional version, instead of ... they allow functions to interact with the React engine; that is, ...

A new feature in React 19 is that a function used as a transition callback can be asynchronous. Such functions are referred to as actions. This allows server calls to be outsourced to a transition ...

Functions are ... from within the function. However, in actual practice, functions often end up needing to interact with the broader context, as evidenced by React’s useEffect hook.