Built-in React APIs

In addition to Hooks and Components, the react package exports a few other APIs that are useful for defining components. This page lists all the remaining modern React APIs.

• createContext lets you define and provide context to the child components. Used with useContext.
• lazy lets you defer loading a component's code until it's rendered for the first time.
• memo lets your component skip re-renders with same props. Used with useMemo and useCallback.
• startTransition lets you mark a state update as non-urgent. Similar to useTransition.
• act lets you wrap renders and interactions in tests to ensure updates have processed before making assertions.

Resource APIs

Resources can be accessed by a component without having them as part of their state. For example, a component can read a message from a Promise or read styling information from a context.

To read a value from a resource, use this API:

• use lets you read the value of a resource like a Promise or context.

function MessageComponent({ messagePromise }) {
  const message = use(messagePromise);
  const theme = use(ThemeContext);
  // ...
}