feat: Try out some simple preloading

plugins/preload.js

@@ -0,0 +1,48 @@
+import { promises as fs } from 'node:fs';
+import path from 'node:path';
+
+/**
+ * @returns {import('vite').Plugin}
+ */
+export function preloadPlugin() {
+	return {
+		name: 'preload-plugin',
+		async closeBundle() {
+			const [manifestContent, replContent, assetsDir] = await Promise.all([
+				fs.readFile(path.resolve('build', '.vite/manifest.json'), 'utf-8'),
+				fs.readFile(path.resolve('build', 'repl/index.html'), 'utf-8'),
+				fs.readdir(path.resolve('build', 'assets'))
+			]);
+
+			const replWorker = `assets/${assetsDir.find((file) => file.startsWith('repl.worker-'))}`;
+
+			const manifest = JSON.parse(manifestContent);
+
+			let errorOverlay = '';
+			for (const file in manifest) {
+				if (manifest[file].name == 'error-overlay') {
+					errorOverlay = file;
+					break;
+				}
+			}
+
+			const preloadTags = [
+				'src/components/controllers/repl-page.jsx',
+				'src/components/controllers/repl/runner.jsx',
+				'src/components/code-editor/index.jsx',
+				errorOverlay,
+				replWorker
+			].map((file) => {
+				const filePath = manifest[file] ? manifest[file].file : file;
+				return `\n\t\t<link rel="modulepreload" href="/${filePath}"></link>`;
+			}).join('');
+
+			const replWithPreload = replContent.replace(
+				'</head>',
+				`${preloadTags}</head>`
+			);
+
+			await fs.writeFile(path.resolve('build', 'repl/index.html'), replWithPreload);
+		}
+	};
+}

vite.config.js

@@ -9,6 +9,7 @@ import { netlifyPlugin } from './plugins/netlify.js';
 import { spaFallbackMiddlewarePlugin } from './plugins/spa-fallback-middleware.js';
 import { htmlRoutingMiddlewarePlugin } from './plugins/html-routing-middleware.js';
 import { rssFeedPlugin } from './plugins/rss-feed.js';
+import { preloadPlugin } from './plugins/preload.js';
 
 // TODO: Should we do this for all routes, rely on discovery a bit less?
 import { tutorialRoutes } from './src/lib/route-utils.js';
@@ -20,7 +21,8 @@ export default defineConfig({
 	},
 	build: {
 		target: ['chrome88', 'edge88', 'es2020', 'firefox78', 'safari14'],
-		outDir: 'build'
+		outDir: 'build',
+		manifest: true
 	},
 	plugins: [
 		replace({
@@ -58,6 +60,7 @@ export default defineConfig({
 		netlifyPlugin(),
 		spaFallbackMiddlewarePlugin(),
 		htmlRoutingMiddlewarePlugin(),
-		rssFeedPlugin()
+		rssFeedPlugin(),
+		preloadPlugin()
 	]
 });