handling errors from mutate()

[jonathanstanley]

I appreciate the library! From the docs, it isn't clear if there is a proper way to handle exceptions thrown during mutate()

Suppose I want a user's action to trigger a mutation for a specific key (keeping a static key enables sharing between different components). I may want the resulting data or error kept within the swr. For example:

let mySWR = useSWR("myKey");
mySWR.mutate(fetchFromAPI).catch((e) => {});
console.log(mySWR.data, mySWR.error)
//if `fetchFromApi` returns a result, `mySWR.data` should have the result and error is undefined
//if `fetchFromApi` throws an error, `mySWR.error` should have the error text and data is undefined

But that doesn't quite work. Here is my example: https://codesandbox.io/s/swr-mutate-error-user-example-mxp14

Some problems:

1. Depending on whereconsole.log(mySWR) runs, it may show the correct error, or it may hold a random SyntaxError: Unexpected token < in JSON at position 0
2. If I try to conditionally show the error or data, SWR starts running excessive re-validations

Thoughts ?

[shuding]

Thank you for your codesandbox link! The cause of SyntaxError: Unexpected token < in JSON at position 0 is that your useSWR doesn't have fetcher passed in. So it uses the default fetch function, which can't fetch the key since it's not a URL.

You can do this:

useSWR('key', null)

to avoid that behavior.

[jonathanstanley]

thank you