Improve internal API

src/config/rollup.ts

@@ -0,0 +1,53 @@
+import { dev, src, dest } from './env';
+
+export default {
+	dev,
+
+	client: {
+		input: () => {
+			return `${src}/client.js`
+		},
+
+		output: () => {
+			let dir = `${dest}/client`;
+			if (process.env.SAPPER_LEGACY_BUILD) dir += `/legacy`;
+
+			return {
+				dir,
+				entryFileNames: '[name].[hash].js',
+				chunkFileNames: '[name].[hash].js',
+				format: 'esm',
+				sourcemap: dev
+			};
+		}
+	},
+
+	server: {
+		input: () => {
+			return {
+				server: `${src}/server.js`
+			};
+		},
+
+		output: () => {
+			return {
+				dir: `${dest}/server`,
+				format: 'cjs',
+				sourcemap: dev
+			};
+		}
+	},
+
+	serviceworker: {
+		input: () => {
+			return `${src}/service-worker.js`;
+		},
+
+		output: () => {
+			return {
+				file: `${dest}/service-worker.js`,
+				format: 'iife'
+			}
+		}
+	}
+};