Question to snapshot.getPromise vs snapshot.getLoadable

[miracle0930]

Hi team! Currently, I am confused with the snapshot.getPromise and snapshot.getLoadable method. To me these two methods are both used for getting a snapshot from an atom or a selector. The main difference is getPromise is async and getLoadable is sync.

The way I am using them is quite the same, for example

const useSomeCallback = () => {
    return useRecoilCallback(() => async ({ snapshot }) => {
        // use getPromise
        const aSnapshotFromPromise = await snapshot.getPromise(someAtomOrSelector)
        // use getLoadable
        const aSnapshotFromLoadable = snapshot.getLoadable(someAtomOrSelector).getValue()
        // some business logic...
    })
}

In most cases, both two work but sometimes it may different, sometimes getPromise may throw the got null or unexpected crash.

I am wondering what's the main difference between these two methods and when I should consider using getPromise and when I should consider using getLoadable?

Thanks in advance for your help!

[drarmstr]

As you point out they are very similar. getLoadable() is synchronous and returns a Loadable object which encodes the state and either the value, error, or promise to an async value. getPromise() on the other hand returns an async promise to the value, even if the value is synchronous or rejected to the error. You may wish to use the getLoadable() version if you want to synchronously handle the result, error, or pending state.