Two <TempInput> components need to stay in sync (celsius and fahrenheit). Lift the temperature into a <TempConverter> parent and pass a setter down to both children.

What is the exact problem Context solves, and what is the cost of using it? Two sentences.

Build a ThemeProvider with a context exposing the current theme and a switcher, then consume it inside a <ThemedButton> using useContext.

In a legacy class component, how do you read context without useContext? Show the contextType pattern.

Combine useReducer and useContext to expose a tiny <TodosProvider> plus a useTodos() hook. The hook returns { todos, add, toggle }.

A Context value of { user, setUser } is rebuilt on every parent render. Every consumer in the tree re-renders even when user is the same object as before. What is the fix?