vercel/swr · error · Error

Can’t trigger the mutation: missing fetcher.

Error message

Can’t trigger the mutation: missing fetcher.

What it means

Error "Can’t trigger the mutation: missing fetcher." thrown in vercel/swr.

Source

Thrown at src/mutation/index.ts:53

    const [stateRef, stateDependencies, setState] = useStateWithDeps<{
      data: Data | undefined
      error: Error | undefined
      isMutating: boolean
    }>({
      data: UNDEFINED,
      error: UNDEFINED,
      isMutating: false
    })

    const currentState = stateRef.current

    const trigger = useCallback(
      async (arg: any, opts?: SWRMutationConfiguration<Data, Error>) => {
        const [serializedKey, resolvedKey] = serialize(keyRef.current)

        if (!fetcherRef.current) {
          throw new Error('Can’t trigger the mutation: missing fetcher.')
        }
        if (!serializedKey) {
          throw new Error('Can’t trigger the mutation: missing key.')
        }

        // Disable cache population by default.
        const options = mergeObjects(
          mergeObjects(
            { populateCache: false, throwOnError: true },
            configRef.current
          ),
          opts
        )

        // Trigger a mutation, and also track the timestamp. Any mutation that happened
        // earlier this timestamp should be ignored.
        const mutationStartedAt = getTimestamp()

View on GitHub (pinned to 7173e55b2a)

When it happens

Trigger: Thrown at src/mutation/index.ts:53 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of vercel/swr@7173e55b2a (2026-08-27). Data as JSON: /api/errors/9379bccc6a42a718. Report an issue: GitHub.