Set HTTP Content-Type header on JSON response

src/routes/api/contact.ts

@@ -110,7 +110,10 @@ export class Handler {
 					statusText: 'Bad Request',
 				}),
 				{
-					headers: new Headers(DEFAULT_HEADERS),
+					headers: new Headers({
+						...DEFAULT_HEADERS,
+						'Content-Type': 'application/json',
+					}),
 					status: 400,
 				},
 			)
@@ -134,7 +137,10 @@ export class Handler {
 						statusText: 'Bad Request',
 					}),
 					{
-						headers: new Headers(DEFAULT_HEADERS),
+						headers: new Headers({
+							...DEFAULT_HEADERS,
+							'Content-Type': 'application/json',
+						}),
 						status: 400,
 					},
 				)
@@ -171,7 +177,13 @@ export class Handler {
 					})
 				: response.statusText
 		return new Response(body, {
-			headers: new Headers({ ...DEFAULT_HEADERS, ...(response.headers ?? {}) }),
+			headers: new Headers({
+				...DEFAULT_HEADERS,
+				...(response.headers ?? {}),
+				...('bodyFields' in response
+					? { 'Content-Type': 'application/json' }
+					: {}),
+			}),
 			status: response.status,
 		})
 	}

tests/unit/routes/api/contact.test.ts

@@ -100,6 +100,11 @@ describe(PATH, () => {
 						).not.toBeNull(),
 				)
 
+				it('should return json content', async () =>
+					expect(
+						(await handler(request, {} as Context)).headers.get('Content-Type'),
+					).toBe('application/json'))
+
 				it('should return an error message in the body', async () =>
 					expect(
 						await (await handler(request, {} as Context)).json(),
@@ -177,6 +182,16 @@ describe(PATH, () => {
 							await (await handler(request, {} as Context)).json(),
 						).toHaveProperty(property)
 					})
+
+					it('should return json content', async () => {
+						const request = new Request(ROUTE, { body, headers, method })
+
+						expect(
+							(await handler(request, {} as Context)).headers.get(
+								'Content-Type',
+							),
+						).toBe('application/json')
+					})
 				})
 
 				describe('when all required fields are valid', () => {
@@ -317,6 +332,16 @@ describe(PATH, () => {
 								},
 							)
 
+							it('should return json content', async () => {
+								const request = new Request(ROUTE, { body, headers, method })
+
+								expect(
+									(
+										await new Handler(storage).handle(request, {} as Context)
+									).headers.get('Content-Type'),
+								).toBe('application/json')
+							})
+
 							it('should return a message in the body', async () => {
 								const request = new Request(ROUTE, { body, headers, method })