Migrate fullstack app from CJS to ESM (#638)

Author: chvmvd

docs/4-advanced/02-bundler/_samples/fullstack-app/package.json

@@ -3,7 +3,7 @@
   "private": true,
   "version": "0.0.0",
   "scripts": {
-    "start": "node server/main.js",
+    "start": "node server/main.mjs",
     "build": "vite build client --outDir ../dist",
     "prestart": "npm run build"
   },

…er/_samples/fullstack-app/server/main.js …r/_samples/fullstack-app/server/main.mjsdocs/4-advanced/02-bundler/_samples/fullstack-app/server/main.js renamed to docs/4-advanced/02-bundler/_samples/fullstack-app/server/main.mjs docs/4-advanced/02-bundler/_samples/fullstack-app/server/main.js renamed to docs/4-advanced/02-bundler/_samples/fullstack-app/server/main.mjs

@@ -1,4 +1,4 @@
-const express = require("express");
+import express from "express";
 const app = express();
 
 app.use(express.json());

docs/4-advanced/02-bundler/index.mdx

@@ -141,7 +141,7 @@ app
 ├── package.json
 ├── package-lock.json
 └── server
-    └── main.js
+    └── main.mjs
 ```
 
 <ViewSource url={import.meta.url} path="_samples/fullstack-app" />
@@ -151,16 +151,16 @@ app
 ```json title="/package.json"
 {
   "scripts": {
-    "start": "node server/main.js",
+    "start": "node server/main.mjs",
     "build": "vite build client --outDir ../dist"
   }
 }
 ```
 
 `express.static` により Vite が作成したディレクトリを指定すれば完成です。
 
-```javascript title="server/main.js"
-const express = require("express");
+```javascript title="server/main.mjs"
+import express from "express";
 const app = express();
 
 app.use(express.json());