服务器端代码无法识别我的 req.body.variable，说明它未定义

Question

我正在创建一个 Web 应用程序，该应用程序应在每次按下特定按钮时将信息从客户端发送到服务器端。当我按下按钮时，终端继续告诉我我试图通过 post 请求正文传递的值是未定义的。

客户端代码（从哪里调用按钮）-

function upvote(elem) {
  var parentID = elem.parentNode.id;
  console.log('Upvote button was clicked' + parentID);

  fetch('/upvote', {     //This is called to pass the body data to server side code
    method: 'post',
    body: JSON.stringify({
      id: parentID
    })
  })
  .then(function(res) {
    if(res.ok) {
      console.log('Click was recorded');
      return;
    }
    throw new Error('Request failed.');
  })
  .catch(function(error) {
    console.log(error);
  });
}

function downvote(elem){
  var parentID = elem.parentNode.id;
  console.log('Downvote button was clicked');

  fetch('/downvote', {  //This is called to pass the body data to server side code
    method: 'POST',
    body: JSON.stringify({
      id: parentID })
  })
  .then(function(res) {
    if(res.ok) {
      console.log('Click was recorded');
      return;
    }
    throw new Error('Request failed.');
  })
  .catch(function(error) {
    console.log(error);
  });
}

setInterval(function() {
  fetch('/ranking', {method: 'GET'})
    .then(function(response) {
      if(response.ok) return response.json();
      throw new Error('Request failed.');
    })
    .then(function(data) {

    })
    .catch(function(error) {
      console.log(error);
    });
}, 1000);

我的 app.js（服务器端代码）--

const bodyParser = require('body-parser');
const mysql = require('mysql');
const path = require('path');
const app = express();

const {getLoginPage, login} = require('./routes/index');    
const {players, questionsPage, upvoteQues, downvoteQues, ranking, addQuestionsPage, addQuestion, deleteQuestion, editQuestion, editQuestionPage} = require('./routes/question');  //All my routes
const port = 5000;

const db = mysql.createConnection ({
    host: 'localhost',
    user: 'root',
    password: '',
    database: ''
});

// connect to database
db.connect((err) => {
    if (err) {
        throw err;
    }
    console.log('Connected to database');
});
global.db = db;

// configure middleware
app.set('port', process.env.port || port); port
app.set('views', __dirname + '/views'); folder to render our view
app.set('view engine', 'ejs'); 
app.use(bodyParser.urlencoded({ extended: false }));
app.use(bodyParser.json()); 
app.use(express.static(__dirname + '/public'));




app.get('/', getLoginPage);
app.get('/questions', questionsPage);
app.get('/add', addQuestionPage);
app.get('/edit/:id', editQuestionPage);
app.get('/delete/:id', deleteQuestion);
app.get('/ranking', ranking);
app.post('/', login);
app.post('/add', addQuestion);
app.post('/edit/:id', editQuestion);
app.post('/upvote', upvoteQues);     //This is then used 
app.post('/downvote', downvoteQues);  //This is then used 


// set the app to listen on the port
app.listen(port, () => {
    console.log(`Server running on port: ${port}`);
});

我的question.js（更多服务器端代码，只是分成不同的文件）

const fs = require('fs');

module.exports = {
    questionsPage:(req, res) =>{
        let query = "SELECT * FROM `Questions` ORDER BY Ranking DESC"; 

        db.query(query, (err, result) => {
            if (err) {
                console.log('Query error');
                res.redirect('/');
            }
            res.render('questions.ejs', {
                title: "JustAsk!",   
                questions: result,
            });
        });
    },
    upvoteQues: (req, res) => {
        console.log(req.body.id);       //Error here
        let updateQuery = "UPDATE `Questions` Ranking = Ranking+1 WHERE QuestionID = '"+ req.body.id + "'"      //Error here
        db.query(updateQuery, (err, result) => {
            if(err){
                console.log('Query error');
                res.redirect('/players')
            }
        });
    },
    downvoteQues: (req, res) =>{
        console.log(req.body.id);      //Error here
        let updateQuery = "UPDATE `Questions` Ranking = Ranking+1 WHERE QuestionID = '"+ req.body.id + "'"       //Error here
        db.query(updateQuery, (err, result) => {
            if(err){
                console.log('Query error');
                res.redirect('/players')
            }
        });
    }, 
    ranking: (req, res) => {
        let query = "SELECT * FROM `Questions` ORDER BY Ranking DESC"; 
        db.query(query, (err, result) => {
            if (err) {
                console.log('Query error');
            }
            res.send(result);
        });
    }
};

Answer 1

正文应该是 JSON 格式，而不是字符串。

 body: JSON.stringify({
      id: parentID 
})

改为：

 body: { id: parentID }

and content type should be 'application/json` like below.

fetch('/url', {
    method: 'POST',
    body: {id: parentID },
    headers: {
            "Content-Type": "application/json",
    }
  })