Can't catch error using mutate()

[yqz0203]

Bug report

Description / Observed Behavior

If using mutate without parameters, mutate() always return data even if network has been shut down, the error can not be catch.

This is a pseudo-code example below. In this case, If refresh data when pull down, I can't display an error message to user.

const { mutate } = useSWR('foo', ()=>fetch('my link'))

return <List onPullRefresh={()=>{
    mutate().then((data)=>{ 
        console.log(data);
    }).catch((e)=>{ 
        toast.show(e.message);
    });
} />

Expected Behavior

I hope to get the error which was thrown while fetching in catch.

[promer94]

you can use the error from swr result or using config callback

const { mutate, error } = useSWR('foo', ()=>fetch('my link'), { onError: (error) => { console.log(error) } })

see: https://codesandbox.io/s/get-from-result-or-callback-02bxw1

[shuding]

I think generally, we need to think again about our error APIs of mutate(): should it throw right away or set the error state, or both? I'd like to keep this issue open for tracking.

[rebelwolfson]

Good time of day! Facing the same issue.

It sounds like it makes sense for mutate to be able to bypass mutation callback error to handle it via catch individually. The reason is that you are not always using mutate in conjunction with useSWR. It will be annoying to track mutation error only via state hook.

To keep mutate backwards compatibility, new option, like bypassError could be introduced, that is false by default. So the current behavior will stay the same.

Thank you!

[rebelwolfson]

Oh, btw, I was speaking about unbounded mutate function...