# withJsonBody

## withJsonBody()

Wraps a fetch function to automatically stringify plain-object and array bodies as JSON and set the `Content-Type: application/json` header.

```js
import {withJsonBody} from 'fetch-extras';

const fetchWithJson = withJsonBody()(fetch);

const response = await fetchWithJson('/api/users', {
	method: 'POST',
	body: {name: 'Alice', age: 30},
});
// Sends JSON.stringify({name: 'Alice', age: 30}) with Content-Type: application/json
```

## Returns

A function that accepts a fetch function and returns a wrapped fetch function that auto-serializes JSON bodies.

> [!NOTE]
> Only plain objects (`{}`) and arrays are auto-serialized. Other body types like strings, `FormData`, `Blob`, and `ReadableStream` are passed through unchanged.

> [!TIP]
> If you need a custom `Content-Type` (e.g., `application/vnd.api+json`), set it explicitly in the request headers and it will not be overridden.

> [!NOTE]
> When replacing the body of an existing `Request`, the original request `Content-Type` is not preserved. Set the replacement `Content-Type` in `init.headers` or with `withHeaders()` if you need one.

## Example

Can be combined with other `with*` functions:

```js
import {pipeline, withJsonBody, withBaseUrl, withHttpError} from 'fetch-extras';

const apiFetch = pipeline(
	fetch,
	withBaseUrl('https://api.example.com'),
	withJsonBody(),
	withHttpError(),
);

const response = await apiFetch('/users', {
	method: 'POST',
	body: {name: 'Alice'},
});
```