如何修复与Node.js服务器的连接错误？

Question

我正在尝试使此全栈Web应用程序正常工作。每当我运行服务器时，它都会说它已连接，但是当我尝试在浏览器（Google Chrome）上加载该网站时，它将加载几分钟，然后我在屏幕上收到此消息，提示“该页面无法正常工作本地主机未发送任何数据“ ERR_EMPTY_RESPONSE”。这很奇怪，因为我没有在前端或后端的终端上收到任何错误。

这是我的server.js文件：

    const express = require('express');

    const PORT = process.env.PORT || 8080;

    const app = express();

    app.use(express.static('public'));

    app.use(express.urlencoded({ extended: true }));
    app.use(express.json());

    const exphbs = require('express-handlebars');

    app.engine("handlebars", exphbs({ defaultLayout: "main" }));
    app.set("view engine", "handlebars");

    const routes = require('./controllers/wh40k_controllers');

    app.use(routes);

    app.listen(PORT, function() {
        console.log("Server listening on: http://localhost:" + PORT);
    });

这是我的控制器文件：

    const express = require('express');

    const wh40k = require('../models/wh40k');

    const router = express.Router();


    router.get("/", function(req, res) {
         wh40k.selectAll(function(data) {
             let hbsObject = {
                wh40k: data
             };
            console.log(hbsObject);
            res.render("index", hbsObject);
        });
     });

    router.post("/api/wh40k", function(req, res) {
        wh40k.insertOne(["figure_name", "faction", "role", "own"], 
    [req.body.figureName, req.body.faction, req.body.role, req.body.own], 
    function(data) {
            res.json({ figure_name: data.insertName });
        });
    });

    router.put("/api/wh40k/:name", function(req, res) {
        let condition = "name = " + req.params.figure_name;

        wh40k.updateOne(
            {
                figure_name: req.body.figure_name,
                faction: req.body.faction,
                role: req.body.role,
                own: req.body.own
            },
            condition,
            function(result) {
                if(result === 0) {
                    return res.status(404).end();
                }
                res.status(200).end();
            }
        );
    });

    module.exports = router;

这是我的连接文件：

    const mysql = require('mysql');

    const connection = mysql.createConnection({
        host: "localhost",
        port: 8889,
        user: "root",
        password: "root",
        database: "wh40k_db"
     });

    function handleDisconnect() {
      connection = mysql.createConnection(db_config);
    }

    connection.connect(function(err) {          
      if (err) {
        console.log('error when connecting to db:', err);
        setTimeout(handleDisconnect, 2000);
      }
    });

    connection.on('error', function(err) {
      console.log('db error', err);
      if(err.code === 'PROTOCOL_CONNECTION_LOST') { 
        handleDisconnect();                         
      } else {                                      
        throw err;                                  
      }
    });

     module.exports = connection;

这是我的模型文件：

    const orm = require('../config/orm.js');

    let wh40k = {
        selectAll: function(cb) {
            orm.selectAll("figures", function(res) {
                cb(res);
            });
        },
        insertOne: function(cols, vals, cb) {
            orm.insertOne("figures", cols, vals, function(res) {
                cb(res);
            });
        },
        updateOne: function(obj, condition, cb) {
            orm.updateOne("figures", obj, condition, function(res) {
                cb(res);
            });
        }
    };

module.exports = wh40k;

这是我的Orm文件：

    const connection = require('../config/connection.js');

    let orm = {
        selectAll: function(tableSelect) {
            connection.query("SELECT * FROM ??", [tableSelect], function(err, result) {
        if (err) throw err;
        console.log(result);
    });
},
insertOne: function(newInfo, tableSelect) {
    connection.query("INSERT ?? INTO ??", [newInfo, tableSelect], function(err, result) {
        if (err) throw err;
        console.log(result);
    });
},
updateOne: function(updatedInfo, tableSelect) {
    connection.query("UPDATE ?? WHERE ??", [updatedInfo, tableSelect], function(err, result) {
        if (err) throw err;
        console.log(result);
    });
}
    };

    module.exports = orm;

我希望该页面实际上使用MySQL的网页以把手的形式从MySQL数据库中加载信息，但是，如前所述，它不会这样做，而是表示该页面无法加载。