class Loadable

A Loadable object represents the current state of a Recoil atom or selector. This state may either have a value available, may be in an error state, or may still be pending asynchronous resolution. A Loadable has the following interface:

  • state: The current state of the atom or selector. Possible values are 'hasValue', 'hasError', or 'loading'.
  • contents: The value represented by this Loadable. If the state is hasValue, it is the actual value, if the state is hasError it is the Error object that was thrown, and if the state is loading, then you can use toPromise() to get a Promise of the value.

Loadables also contain helper methods for accessing the current state. Consider this API to be unstable:

  • getValue() - Method to access the value that matches the semantics of React Suspense and Recoil selectors. If the state has a value then it returns a value, if it has an error then it throws that error, and if it is still pending then it suspends execution or rendering to propagate the pending state.
  • toPromise(): returns a Promise that will resolve when the selector has resolved. If the selector is synchronous or has already resolved, it returns a Promise that resolves immediately.
  • valueMaybe() - Returns the value if available, otherwise returns undefined
  • valueOrThrow() - Returns the value if available or throws an Error.
  • map() - Takes a function to transform the value of the Loadable and returns a new Loadable with the transformed value. The transformation function gets a parameter of the value and returns the new value; it can also propagate thrown errors or suspense.

Example

function UserInfo({userID}) {
const userNameLoadable = useRecoilValueLoadable(userNameQuery(userID));
switch (userNameLoadable.state) {
case 'hasValue':
return <div>{userNameLoadable.contents}</div>;
case 'loading':
return <div>Loading...</div>;
case 'hasError':
throw userNameLoadable.contents;
}
}