错误 [ERR_HTTP_HEADERS_SENT]：在 Node JS 中将标头发送到客户端后无法设置标头

Question

我正在尝试使用不工作但出现上述错误的特定 ID 更新数据。

更新时，我首先在数据库中搜索该特定 ID，然后将数据保存到 MongoDB

这是我的server.js

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

//importing MongoDB model schema
let ToDo = require('./todo.model');

const app = express();
const todoRoutes = express.Router();

const PORT = 4000;

//middlewares
app.use(bodyParser.json());
app.use(cors());
app.use('/todos', todoRoutes);

//connection to the MongoDB database
mongoose.connect('mongodb://127.0.0.1:27017/todos', {useNewUrlParser: true});
const connection = mongoose.connection;
connection.once('open', () =>{
    console.log("Connected to the MongoDB through port: 27017");
 });

app.listen(PORT, () => { 
    console.log(`Listening to port: ${PORT}`);
});

//get all data - removed to show only the code snippet I am getting errors

//get data by an ID - removed to show only the code snippet I am getting errors

//add items to database -removed to show only the code snippet I am getting errors

//update items
todoRoutes.route('/update/:id').post((req, res) => {
    let id = req.params.id;
    ToDo.findById(id, (err, todo) => {
        if(err) throw err;
        if(!todo) res.status(400).send("No data found");

        todo.todo_description = req.body.todo_description;
        todo.todo_responsible = req.body.todo_responsible;
        todo.todo_priority = req.body.todo_priority;
        todo.todo_completed = req.body.todo_completed;
        res.end();

        todo.save().then(todo => {
            res.json(200).send("Data Updated! " + todo);
            res.end();
        }).catch(err => {
            res.status(400).send("Error occured! " + err);
        });
    });
});

这是我遇到的错误...

有人可以帮帮我吗？

Answer 1

此错误通常意味着您多次发送响应。

请注意，您一个接一个地发送了两个响应 res.json() 和 res.end()

如果您出于某种原因只想结束响应，请使用res.end()，否则使用res.status(200).json({ result: ‘Data updated’ + todo })

如果你同时发送，它会抱怨在发送（通过res.status().json()）后尝试修改响应（通过res.end()）

Answer 2

在'/update/:id' 路由中，您发送res.end()，然后在3 行后再次发送。如果您删除第一个res.end()，它应该可以工作。

如果缺少todo，您还应该return：

todoRoutes.route('/update/:id').post((req, res) => {
    let id = req.params.id;
    ToDo.findById(id, (err, todo) => {
        if(err) throw err;
        if(!todo) return res.status(400).send("No data found");

        todo.todo_description = req.body.todo_description;
        todo.todo_responsible = req.body.todo_responsible;
        todo.todo_priority = req.body.todo_priority;
        todo.todo_completed = req.body.todo_completed;

        todo.save().then(todo => {
            res.status(200).send("Data Updated! " + todo);
        }).catch(err => {
            res.status(400).send("Error occured! " + err);
        });
    });
});