使用Nodemon时Express服务器无法启动或连接的问题求助

我用Express、Node和Nodemon搭建了新项目，完成基础配置后执行npm start，终端只显示启动基础信息，没有服务器运行地址的提示，访问localhost也连不上，不知道问题在哪。

package.json 文件内容 #

{
  "name": "resturant-picker",
  "version": "1.0.0",
  "description": "Resturant picker app for Alchs",
  "main": "server.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "start": "nodemon server.js"
  },
  "repository": {
    "type": "git",
    "url": "git+https://github.com/connordensmore/resturant-picker.git"
  },
  "keywords": [
    "crud",
    "mongodb"
  ],
  "author": "Connor",
  "license": "ISC",
  "bugs": {
    "url": "https://github.com/connordensmore/resturant-picker/issues"
  },
  "homepage": "https://github.com/connordensmore/resturant-picker#readme",
  "dependencies": {
    "axios": "^0.27.2",
    "body-parser": "^1.20.0",
    "dotenv": "^16.0.2",
    "ejs": "^3.1.8",
    "express": "^4.18.1",
    "mongoose": "^6.5.5",
    "morgan": "^1.10.0",
    "node": "^18.8.0",
    "nodemon": "^2.0.19"
  }
}

server.js 文件内容 #

const express = require("express");
const app = express();

const PORT = process.env.PORT || 3000;

app.get("/", (req, res) => {
  res.send("Crud App");

  app.listen(PORT, () => {
    console.log(`Server is running on http://localhost:${PORT}`);
  });
});

执行npm start后的终端响应 #

mopdog@Connors-MacBook-Pro resturant-picker % npm start             

> resturant-picker@1.0.0 start
> nodemon server.js

[nodemon] 2.0.19
[nodemon] to restart at any time, enter `rs`
[nodemon] watching path(s): *.*
[nodemon] watching extensions: js,mjs,json
[nodemon] starting `node server.js`
[nodemon] clean exit - waiting for changes before restart

问题核心是**app.listen()被错误放在了app.get("/")的路由回调内部**：

• Express只有在访问根路径/时才会执行该回调里的代码，但服务器没启动的话根本无法访问/，直接陷入逻辑死循环。
• 因为服务器始终没启动，Node.js执行完顶部代码后就直接退出，所以nodemon提示clean exit，等待文件变更后重启。

修复方法很简单，把app.listen()移出路由回调，放在文件最外层：

const express = require("express");
const app = express();

const PORT = process.env.PORT || 3000;

app.get("/", (req, res) => {
  res.send("Crud App");
});

// 将服务器启动代码移到路由定义之外
app.listen(PORT, () => {
  console.log(`Server is running on http://localhost:${PORT}`);
});

修改后重新执行npm start，就能看到服务器启动的地址提示，访问http://localhost:3000也能正常返回内容。

内容的提问来源于stack exchange，提问作者Connor Densmore