[chore] improve local REPL without local Supabase

sites/svelte.dev/README.md

@@ -1,6 +1,10 @@
 ## Running locally
 
-Setup a database on [Supabase](https://supabase.com) with the instructions [here](../../db) and set the corresponding environment variables.
+A local database is only required in dev mode if you want to test reading and writing saved REPLs on it. Without a local database in dev mode, the REPL will be able to load saved REPLs from the production database, but not save them.
+
+Note also that in dev mode, the REPL will currently only work in Chrome, [as noted in the Vite documentation](https://vitejs.dev/guide/features.html#web-workers), pending support in Firefox for `import` statements in web workers.
+
+If you do want to use a database, set it up on [Supabase](https://supabase.com) with the instructions [here](../../db) and set the corresponding environment variables.
 
 Run the site sub-project:
 

sites/svelte.dev/src/lib/db/client.js

@@ -1,6 +1,8 @@
+import { dev } from '$app/env';
 import { createClient } from '@supabase/supabase-js';
 
-const SUPABASE_URL = process.env['SUPABASE_URL'];
-const SUPABASE_KEY = process.env['SUPABASE_KEY'];
+const SUPABASE_URL = process.env.SUPABASE_URL;
+const SUPABASE_KEY = process.env.SUPABASE_KEY;
 
-export const client = createClient(SUPABASE_URL, SUPABASE_KEY, { fetch });
+export const client =
+	(!dev || (SUPABASE_URL && SUPABASE_KEY)) && createClient(SUPABASE_URL, SUPABASE_KEY, { fetch });

sites/svelte.dev/src/routes/repl/[id]/index.json.js

@@ -1,3 +1,5 @@
+import { dev } from '$app/env';
+import { client } from '$lib/db/client';
 import * as gist from '$lib/db/gist';
 import { API_BASE } from '$lib/env';
 
@@ -58,6 +60,12 @@ export async function get({ params }) {
 		};
 	}
 
+	if (dev && !client) {
+		// in dev with no local Supabase configured, proxy to production
+		// this lets us at least load saved REPLs
+		return fetch(`https://svelte.dev/repl/${params.id}.json`);
+	}
+
 	const app = await gist.read(params.id);
 
 	if (!app) {