Pros — Great to start off with. Less commitment, more immediate reward.
Cons — Annotations feel underpowered — verbose and repetitive, different constructs (than .ts, closer to jsdoc), imports are hard, type assertion and generics don’t work that well, smaller community. Overall, much closer to .d.ts files than a full-blown .ts replacement
React stores its internal representation of the render tree as React Fiber (v16.0+). It create fiber node for each JSX element we have rendered, which are then connected to its parent, child and sibling node to create a complete tree.
We will call this connected tree structure as Fiber tree.
For a rough idea, it contains most of the information that you would find in the React debugger — components tab.