Include charset=utf-8 by default in application/json endpoints. (#1669)

Author: coreh

.changeset/fuzzy-kids-turn.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Use UTF-8 encoding for JSON endpoint responses by default

packages/kit/src/runtime/server/endpoint.js

@@ -54,8 +54,11 @@ export default async function render_route(request, route) {
 			/** @type {import('types/hooks').StrictBody} */
 			let normalized_body;
 
-			if (typeof body === 'object' && (!type || type === 'application/json')) {
-				headers = { ...headers, 'content-type': 'application/json' };
+			if (
+				typeof body === 'object' &&
+				(!type || type === 'application/json' || type === 'application/json; charset=utf-8')
+			) {
+				headers = { ...headers, 'content-type': 'application/json; charset=utf-8' };
 				normalized_body = JSON.stringify(body);
 			} else {
 				normalized_body = /** @type {import('types/hooks').StrictBody} */ (body);

packages/kit/test/apps/basics/src/routes/encoded/_tests.js

@@ -27,4 +27,9 @@ export default function (test) {
 		assert.equal(await page.innerHTML('h2'), '/encoded/苗条');
 		assert.equal(await page.innerHTML('h3'), '/encoded/苗条');
 	});
+
+	test('sets charset on JSON Content-Type', null, async ({ fetch }) => {
+		const response = await fetch('/encoded/endpoint');
+		assert.equal(response.headers.get('content-type'), 'application/json; charset=utf-8');
+	});
 }

packages/kit/test/apps/basics/src/routes/encoded/endpoint.js

@@ -0,0 +1,7 @@
+export async function get() {
+	return {
+		body: {
+			fruit: '🍎🍇🍌'
+		}
+	};
+}

packages/kit/test/apps/basics/src/routes/load/_tests.js

@@ -14,7 +14,7 @@ export default function (test, is_dev) {
 		});
 
 		const payload =
-			'{"status":200,"statusText":"","headers":{"content-type":"application/json"},"body":"{\\"answer\\":42}"}';
+			'{"status":200,"statusText":"","headers":{"content-type":"application/json; charset=utf-8"},"body":"{\\"answer\\":42}"}';
 
 		if (!js) {
 			// by the time JS has run, hydration will have nuked these scripts