我正在尝试将节点应用程序与MongoDB连接。当我得到输出时，代码似乎执行了 服务器在端口5000上运行 MongoDB数据库连接成功建立 在终端上 但是，当我尝试发布失眠症获得诊断信息时，大约需要两分钟 错误：服务器未返回任何内容（无标题，无数据）

const express = require('express');
//const bodyParser = require('body-parser');
const cors =  require('cors');
const mongoose = require('mongoose');

require('dotenv').config();

const app = express();
const port = process.env.PORT || 5000;

app.use(cors());
app.use(express.json());

const uri = process.env.ATLAS_URI;

mongoose.connect( uri,{useUnifiedTopology: true,useNewUrlParser: true},() => { console.log("MongoDB database conection established successfully")}).catch(err => console.log(err));

const exercisesRouter = require('./routes/exercises');
const usersRouter = require('./routes/users');

app.use('/exercises',exercisesRouter);
app.use('/users',usersRouter);

//emitter.setMaxListeners();

app.listen(port,() => {
    console.log('Server is running on port : ' + port);
});

我正在关注一个教程，这些是我拥有的其他文件 exercise.model.js

const mongoose = require('mongoose');

const Schema = mongoose.Schema;

const exerciseSchema = new Schema({
    username: {type: String,required: true},description: {type: String,duration: {type: Number,date: {type: Date,},{
    timestamps: true,});


const Exercise = mongoose.model('Exercise',exerciseSchema);

module.exports = Exercise;

exercises.js

const router = require('express').Router();
let Exercise = require('../models/exercise.model');

router.route('/').get((req,res) => {
  Exercise.find()
    .then(exercises => res.json(exercises))
    .catch(err => res.status(400).json('Error: ' + err));
});

router.route('/add').post((req,res) => {
  const username = req.body.username;
  const description = req.body.description;
  const duration = Number(req.body.duration);
  const date = Date.parse(req.body.date);

  const newExercise = new Exercise({
    username,description,duration,date,});

  newExercise.save()
  .then(() => res.json('Exercise added!'))
  .catch(err => res.status(400).json('Error: ' + err));
});

module.exports = router;

users.js

const router = require('express').Router();
let User = require('../models/user.model');

router.route('/').get((req,res) => {
        User.find()
        .then(users => res.json(users))
        .catch(err => res.status(400).json('Error: ' + err));
    });

router.route('/add').post((req,res) => {
    const username = req.body.username;

    const newUser = new User({username});

    newUser.save()
    .then(() => res.join('User added!'))
    .catch(err => res.status(400).json('Error: ' + err));
})

module.exports = router;

user.model.js

const mongoose = require('mongoose');

    const Schema = mongoose.Schema;

    const userSchema = new Schema({
        username: {
            type: String,required: true,unique: true,trim: true,minlenght: 3
        },{
        timestamps: true,});


    const User = mongoose.model('User',userSchema);

module.exports = User;

当我在浏览器中转到http://localhost:5000时，在检查器错误中，我也收到Cannot GET /消息，它说拒绝加载图像'http://localhost:5000/favicon.ico'，因为它违反了以下内容安全策略指令： “ default-src'none'”。请注意，未明确设置“ img-src”，因此将“ default-src”用作后备。这可能很多，但是我正在尝试学习如何将后端与前端连接起来，如果有人可以指导我，我将不胜感激。谢谢你。