core: deprecate preloadCode calls with multiple arguments (#11266)

related to #11259 and #10398

Author: Rich-Harris

.changeset/warm-impalas-thank.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+chore: deprecate `preloadCode` calls with multiple arguments

packages/kit/src/runtime/client/client.js

@@ -277,6 +277,10 @@ export function create_client(app, target) {
 
 	/** @param {...string} pathnames */
 	async function preload_code(...pathnames) {
+		if (DEV && pathnames.length > 1) {
+			console.warn('Calling `preloadCode` with multiple arguments is deprecated');
+		}
+
 		const matching = routes.filter((route) => pathnames.some((pathname) => route.exec(pathname)));
 
 		const promises = matching.map((r) => {