Released in early 2019

Developers can 'hook' into React state and lifecycle features from functional components.

Hook Rules

Rule 1: "Only call hooks at the top level"

( do not call hooks inside loops, conditions or nested statements ) 

Hooks are called in the same order for each render.

Rule 2: "Only call Hooks from React Functions"

( can't be called from plain JavaScript functions )

( stateful login stays with the component )