Add isJsonContentType predicate to fetchBaseQuery

packages/toolkit/src/query/fetchBaseQuery.ts

@@ -37,8 +37,8 @@ const defaultFetchFn: typeof fetch = (...args) => fetch(...args)
 const defaultValidateStatus = (response: Response) =>
   response.status >= 200 && response.status <= 299
 
-const isJsonContentType = (headers: Headers) =>
-  headers.get('content-type')?.trim()?.startsWith('application/json')
+const defaultIsJsonContentType = (headers: Headers) =>
+  !!headers.get('content-type')?.trim()?.startsWith('application/json')
 
 const handleResponse = async (
   response: Response,
@@ -123,6 +123,15 @@ export type FetchBaseQueryArgs = {
     init?: RequestInit | undefined
   ) => Promise<Response>
   paramsSerializer?: (params: Record<string, any>) => string
+  /**
+   * By default, we only check for 'application/json' as the content-type for json. If you need to support another format, you can pass
+   * in a predicate function for your given api to get the same automatic stringifying behavior
+   * @example
+   * ```ts
+   * const isJsonContentType = (headers: Headers) => ["application/vnd.api+json", "application/json"].includes(headers.get("content-type")?.trim());
+   * ```
+   */
+  isJsonContentType?: (headers: Headers) => boolean
 } & RequestInit
 
 export type FetchBaseQueryMeta = { request: Request; response?: Response }
@@ -162,12 +171,17 @@ export type FetchBaseQueryMeta = { request: Request; response?: Response }
  *
  * @param {(params: Record<string, unknown>) => string} paramsSerializer
  * An optional function that can be used to stringify querystring parameters.
+ * 
+ * @param {(headers: Headers) => boolean} isJsonContentType
+ * An optional predicate function to determine if `JSON.stringify()` should be called on the `body` arg of `FetchArgs`
+
  */
 export function fetchBaseQuery({
   baseUrl,
   prepareHeaders = (x) => x,
   fetchFn = defaultFetchFn,
   paramsSerializer,
+  isJsonContentType = defaultIsJsonContentType,
   ...baseFetchOptions
 }: FetchBaseQueryArgs = {}): BaseQueryFn<
   string | FetchArgs,

packages/toolkit/src/query/tests/fetchBaseQuery.test.tsx

@@ -399,6 +399,34 @@ describe('fetchBaseQuery', () => {
         `${baseUrl}/echo?someArray[]=a&someArray[]=b&someArray[]=c`
       )
     })
+
+    it('should supports a custom isJsonContentType function', async () => {
+      const testBody = {
+        i_should_be_stringified: true,
+      }
+      const baseQuery = fetchBaseQuery({
+        baseUrl,
+        fetchFn: fetchFn as any,
+        isJsonContentType: (headers) =>
+          ['application/vnd.api+json', 'application/json'].includes(
+            headers.get('content-type') ?? ''
+          ),
+      })
+
+      let request: any
+      ;({ data: request } = await baseQuery(
+        {
+          url: '/echo',
+          method: 'POST',
+          body: testBody,
+          headers: { 'content-type': 'application/vnd.api+json' },
+        },
+        commonBaseQueryApi,
+        {}
+      ))
+
+      expect(request.body).toMatchObject(testBody)
+    })
   })
 
   describe('validateStatus', () => {