我正在使用 nodejs 和 express 来构建一个非常简单的服务器，但是每次我更改我的代码时，都会出现该端口已在使用中的错误

Question

每次我对代码做一些更改然后运行出现这个错误我已经更改了很多端口并且不知道它背后的原因。也请解释一下process.env.PORT的含义及其意义，在此先感谢

index.js

/*******installed modules****** */
        const express = require('express')
        const mongoose = require('mongoose')
        const path = require('path')
    
    /*****user created modules******* */
    const User = require('./model/user')
    const PORT = 8005
    
    
    const app = express()
    
    /*********middlewares**********/
    app.use(express.urlencoded({ extended: true }));
    app.use(express.json());
    app.use(express.static('static'))
    
    
    
    
    /******view engine*********** */
    app.set('views', path.join(__dirname, 'views'));
    
    // Set view engine as EJS
    app.engine('html', require('ejs').renderFile);
    app.set('view engine', 'html');
    
    
    
    
    /********connect with mongoDb cloud********/
    const mongoUrl = 'mongodb+srv://admin:{my_key}@cluster0.zskv7.mongodb.net/myFirstDatabase?retryWrites=true&w=majority'
    mongoose.connect(mongoUrl, { useNewUrlParser: true, useUnifiedTopology: true });
    mongoose.connection.on("connected", () => {
        console.log("connected to mongoDb");
    });
    
    
    
    /*********get request to check if server is working properly*********/
    
    app.get('/', (req, res) => {
        res.render('index')
    })
    
    app.use('/favgame', (req, res) => {
        const { name, fav_game } = req.body
        User.find({ name: name })
            .then((oldUser) => {
                if (oldUser) {
                    return res
                        .status(422)
                        .json({ error: "user already exists in the database" });
                }
                //if user does not exists initially
                //create new user with these details
                const user = new User(req.body);
                user
                    .save()
                    .then((user) => {
                        res.json({ message: "successfully saved" })
                        console.log('User saved successfully')
                    })
                    .catch((err) => {
                        res.send("Error", err)
                        console.log('cannot create user some error');
                    });
            })
    })
    
    
    
    
    /**********listening on server************ */
    app.listen(PORT, (err) => {
        if (err) {
            return console.log(err);
        }
        console.log(`Server started on PORT: ${PORT}`);
    })

错误来了

node:events:342
      throw er; // Unhandled 'error' event
      ^

Error: listen EADDRINUSE: address already in use :::8005
    at Server.setupListenHandle [as _listen2] (node:net:1306:16)
    at listenInCluster (node:net:1354:12)
    at Server.listen (node:net:1441:7)
    at Function.listen (/home/dhruv/Desktop/quiz_question/node_modules/express/lib/application.js:618:24)
    at Object.<anonymous> (/home/dhruv/Desktop/quiz_question/index.js:75:5)
    at Module._compile (node:internal/modules/cjs/loader:1109:14)
    at Object.Module._extensions..js (node:internal/modules/cjs/loader:1138:10)
    at Module.load (node:internal/modules/cjs/loader:989:32)
    at Function.Module._load (node:internal/modules/cjs/loader:829:14)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:76:12)
    at node:internal/main/run_main_module:17:47
Emitted 'error' event on Server instance at:
    at emitErrorNT (node:net:1333:8)
    at processTicksAndRejections (node:internal/process/task_queues:83:21) {
  code: 'EADDRINUSE',
  errno: -98,
  syscall: 'listen',
  address: '::',
  port: 8005
}

我已经检查了之前发布在类似标题上的问题，但没有得到帮助，应用这些更改也没有解决错误，我知道错误是非常基本的，但无法弄清楚

Answer 1

您收到此错误是因为程序本身正在运行ning（并使用指定的端口）并且您正在尝试再次运行它，简单的解决方案是先停止程序然后运行再次应用更改，更好的解决方案是使用像 nodemon 这样的热重载帮助程序包，你可以安装它：

npm install -g nodemon

并像这样使用它运行

nodemon index.js

这将停止并重新运行服务器上的代码更改保存。

关于process.env.PORT，process.env一般是环境变量对象，由OS或任何其他填充环境变量的工具定义，环境变量在KEY:VALUE形式 PORT 只是定义环境变量的键，process.env.PORT 产生 PORT 环境变量的值。

我正在使用 nodejs 和 express 来构建一个非常简单的服务器，但是每次我更改我的代码时，都会出现该端口已在使用中的错误

i am using nodejs and express to build a very simple server but every time i changes my code error comes that port already is in use

javascript

backend

node.js

express

web