Why does the mutate method still resolve instead of reject when the request fails?

[lovetingyuan]

I want the mutate method to reject when the fetch api rejects, instead of returning the cached data. At least give me an option to support this feature.

I have a refresh button, I click it to call mutate method, but I can not know whether the api request is success or failed.

[sunnypatell]

@lovetingyuan the behavior depends on how you call mutate(). when you call it with just a key and no data/fetcher argument (like mutate('/api/data')), it triggers a revalidation, but revalidation errors go to the hook's error state rather than rejecting the promise.

to get a rejecting promise, you need to either use the bound mutate from useSWR (which has throwOnError: true by default) or pass a fetcher explicitly:

// option 1: bound mutate (throwOnError defaults to true)
const { mutate } = useSWR('/api/data', fetcher);
try {
  await mutate();
} catch (err) {
  console.error('refresh failed:', err);
}

// option 2: global mutate with explicit fetcher
import { mutate } from 'swr';
try {
  await mutate('/api/data', fetcher('/api/data'), { throwOnError: true });
} catch (err) {
  console.error('refresh failed:', err);
}

the key distinction is that bare mutate(key) only signals "please revalidate" and the error flows through the hook's reactive state. passing a fetcher/promise makes mutate own the request lifecycle and properly reject on failure.

ref: SWR mutation docs

[lovetingyuan]

thanks so much