Add NextApiHandler type (#10573)

* Add NextApiHandler type

* Fix formatting
Co-authored-by: NJoe Haddad <timer150@gmail.com>

packages/next/next-server/lib/utils.ts

@@ -219,6 +219,14 @@ export type NextApiResponse<T = any> = ServerResponse & {
   clearPreviewData: () => NextApiResponse<T>
 }
 
+/**
+ * Next `API` route handler
+ */
+export type NextApiHandler<T = any> = (
+  req: NextApiRequest,
+  res: NextApiResponse<T>
+) => void
+
 /**
  * Utils
  */

packages/next/types/index.d.ts

@@ -9,6 +9,7 @@ import {
   NextComponentType,
   NextApiResponse,
   NextApiRequest,
+  NextApiHandler,
   // @ts-ignore This path is generated at build time and conflicts otherwise
 } from '../dist/next-server/lib/utils'
 
@@ -53,6 +54,12 @@ export type PageConfig = {
   }
 }
 
-export { NextPageContext, NextComponentType, NextApiResponse, NextApiRequest }
+export {
+  NextPageContext,
+  NextComponentType,
+  NextApiResponse,
+  NextApiRequest,
+  NextApiHandler,
+}
 
 export default next