Error Handling

Overview

If your query or mutation happens to throw an error when using fetchBaseQuery, it will be returned in the error property of the respective hook. The component will re-render when that occurs, and you can show appropriate UI based on the error data if desired.

Error Display Examples

Query Error

function PostsList() {
  const { data, error } = useGetPostsQuery()

  return (
    <div>
      {error.status} {JSON.stringify(error.data)}
    </div>
  )
}

Mutation Error

function AddPost() {
  const [addPost, { error }] = useAddPostMutation()

  return (
    <div>
      {error.status} {JSON.stringify(error.data)}
    </div>
  )
}

tip

If you need to access the error or success payload immediately after a mutation, you can chain .unwrap().

Using .unwrap

addPost({ id: 1, name: 'Example' })
  .unwrap()
  .then((payload) => console.log('fulfilled', payload))
  .catch((error) => console.error('rejected', error))

Manually selecting an error

function PostsList() {
  const { error } = useSelector(api.endpoints.getPosts.select())

  return (
    <div>
      {error.status} {JSON.stringify(error.data)}
    </div>
  )
}

Errors with a custom baseQuery

Whether a response is returned as data or error is dictated by the baseQuery provided.

Ultimately, you can choose whatever library you prefer to use with your baseQuery, but it's important that you return the correct response format. If you haven't tried fetchBaseQuery yet, give it a chance! Otherwise, see Customizing Queries for information on how to alter the returned errors.

Handling errors at a macro level

There are quite a few ways that you can manage your errors, and in some cases, you may want to show a generic toast notification for any async error. Being that RTK Query is built on top of Redux and Redux-Toolkit, you can easily add a middleware to your store for this purpose.

tip

Redux Toolkit has action matching utilities that we can leverage for additional custom behaviors.

Error catching middleware example

import { isRejectedWithValue } from '@reduxjs/toolkit'
import type { MiddlewareAPI, Middleware } from '@reduxjs/toolkit'
import { toast } from 'your-cool-library'

/**
 * Log a warning and show a toast!
 */
export const rtkQueryErrorLogger: Middleware =
  (api: MiddlewareAPI) => (next) => (action) => {
    // RTK Query uses `createAsyncThunk` from redux-toolkit under the hood, so we're able to utilize these matchers!
    if (isRejectedWithValue(action)) {
      console.warn('We got a rejected action!')
      toast.warn({
        title: 'Async error!',
        message:
          'data' in action.error
            ? (action.error.data as { message: string }).message
            : action.error.message,
      })
    }

    return next(action)
  }