# Error Handling

 

## Error Handling

### Overview

If your query or mutation happens to throw an error when using [fetchBaseQuery](https://github.com/bgoonz/Learning-Redux/blob/master/repos/redux-toolkit/docs/rtk-query/api/fetchBaseQuery/README.md), 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

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

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

```tsx
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()`.

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

:::

```tsx
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`](https://github.com/bgoonz/Learning-Redux/blob/master/repos/redux-toolkit/docs/rtk-query/api/fetchBaseQuery/README.md) yet, give it a chance! Otherwise, see [Customizing Queries](https://github.com/bgoonz/Learning-Redux/blob/master/repos/redux-toolkit/docs/rtk-query/usage/customizing-queries/README.md) 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](/my-docs/redux/repos/redux-toolkit/docs/api/matching-utilities.md#matching-utilities) that we can leverage for additional custom behaviors.

:::

```ts
import {
  MiddlewareAPI,
  isRejectedWithValue,
  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 use matchers!
  if (isRejectedWithValue(action)) {
    console.warn('We got a rejected action!')
    toast.warn({ title: 'Async error!', message: action.error.data.message })
  }

  return next(action)
}
```


---

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