ich mit einem Express-Backend bin mit reagieren Frontend alles gut funktioniert, aber gelegentlich bekomme ich FehlerCant gesetzt Header, nachdem sie
Cant Set-Header, nachdem sie
gesendet werden und Server bekommt down.i suchte einige Möglichkeiten, wie dieser Fehler passieren könnte, aber in meinem Code konnte ich solche Fälle nicht finden.Ich versuchte, so einfach wie möglich im Code zu sein.Kann jemand bitte zeigen Sie mir, was könnte das Problem sein?
Server.js Datei
// call the packages we need
const addItem = require('./controllers/addItem');
const addCategory = require('./controllers/addCategory');
const addSubCategory = require('./controllers/addSubCategory');
const getSubCategory = require('./controllers/getSubCategoryByCategory');
const getCategory = require('./controllers/getAllCategory');
const getAllItems = require('./controllers/getAllItems');
const cors = require('cors');
const express = require('express');
// call express
const app = express(); // define our app using express
const bodyParser = require('body-parser');
// configure app to use bodyParser()
// this will let us get the data from a POST
app.use(bodyParser.urlencoded({ extended: true }));
app.use(bodyParser.json());
app.use(cors());
const port = process.env.PORT || 8080; // set our port
// ROUTES FOR OUR API
// =============================================================================
const addItemRoute = express.Router(); // get an instance of the express Router
const getCategoryRoute = express.Router();
const addCategoryRoute = express.Router();
const addSubCategoryRoute = express.Router();
const getSubCategoryRoute = express.Router();
const getAllItemsRoute = express.Router();
getCategoryRoute.get('/get_category', (req, res) => {
getCategory(res);
});
addCategoryRoute.post('/add_category', (req, res) => {
addCategory(req.body.name, res);
});
getSubCategoryRoute.get('/get_subcategory/:catId', (req, res) => {
getSubCategory(req.params.catId, res);
});
addSubCategoryRoute.post('/add_subcategory', (req, res) => {
addSubCategory(req.body.name, req.body.cat_id, res);
});
// code, name, quantity, length, description and subcategory id should be passed as parameters
addItemRoute.post('/add_item', (req, res) => {
addItem(req.body.item, res);
});
getAllItemsRoute.get('/get_items', (req, res) => {
getAllItems(res);
});
// more routes for our API will happen here
// REGISTER OUR ROUTES -------------------------------
// all of our routes will be prefixed with /api
app.use('/api', addItemRoute);
app.use('/api', getCategoryRoute);
app.use('/api', addCategoryRoute);
app.use('/api', addSubCategoryRoute);
app.use('/api', getSubCategoryRoute);
app.use('/api', getAllItemsRoute);
// START THE SERVER
// =============================================================================
app.listen(port);
console.log(`Server started on port ${port}`);
getAllCategories() Funktion
Object.defineProperty(exports, '__esModule', {
value: true,
});
const pool = require('./connection');
module.exports = function (res) {
pool.getConnection((err, connection) => {
if (err) {
connection.release();
return res.json({ code: 100, status: 'Error in connection database' });
}
console.log(`connected as id ${connection.threadId}`);
connection.query('select * from category;', (err, rows) => {
connection.release();
if (!err) {
return res.json(rows);
}
});
connection.on('error', err => res.json({ code: 100, status: 'Error in connection database' }));
});
};