Introducing a React Hook
The state is mostly local to a component, at least as far as this book is mostly concerned. The natural place for storage would be under a component instance because a component in React defines a piece of UI. So, where is the component instance of a function component in React stored?
It turns out that a component isn't the smallest unit in React. There's a more granular structure called fiber, which is used to represent a piece of element. A fiber performs all the tasks for this element. The element can be as simple as h1, div elements, or it can be an artificial element that does things differently. For instance, a "fragment" element can group other elements without displaying itself, or a "memo" element can remember all the elements from the last update.
Actually, a function component is one of the artificial elements that a fiber represents. What a function component does is allow us to define what elements it can display...
