Handling POST and GET requests in Express - express

Question

First time using express here.
I have the following in my app.js file:
const express = require("express");
const mysql = require("mysql");
const app = express();
const PORT = process.env.PORT || 8000;
const connection = mysql.createConnection({
host: "localhost",
user: "admin",
password: "password",
database: "mydb",
});
app.use(express.static(__dirname + "/express"));
app.use(express.urlencoded()); // have also tried with "extended: true" and "extended: false"
app.use(express.json());
// GET
app.get("/getAllUserActivity", (req, res) => {
const order = req.query.order || "id";
const page = req.query.page || 0;
const limit = req.query.limit || 100;
connection.connect((err) => {
if (err) throw err;
connection.query(
"SELECT id, username, counter FROM users ORDER BY ? LIMIT ?,?",
[order, page, limit],
(err, results, fields) => {
if (err) throw err;
res.send(results);
}
);
});
});
// POST
app.post("/updateUserActivity", (req, res) => {
const userId = req.body.userId;
const username = req.body.username;
const counter = req.body.counter;
connection.connect((err) => {
if (err) throw err;
connection.query(
"INSERT INTO users (id, username, counter) VALUES (?, ?) ON DUPLICATE KEY UPDATE counter = counter + ?",
[userId, username, counter],
(err, results, fields) => {
if (err) throw err;
res.send(results);
}
);
});
});
My POST requests have the header "Content-Type": "application/x-www-form-urlencoded".
The issue I am facing is two-fold:
The GET request fails every other time. First time it returns the expected data, but the second time I get Incomplete response received from application - repeat.
I can only get either the POST or the GET request to work - depending on how I setup the middleware. How can I have both GET and POST here?
Old php user here, trying to figure out Express. Thanks!

Answer 1

Replace all if (err) throw err; with sending an actual error response back to the client. You MUST always send some form of response to every incoming request. It is a shame that many pieces of demo code show that if (err) throw err; because inside an asynchronous callback, that is pretty much never the correct code.
Then (though I don't know the specific details of your database) you will need to release/close your database connections after using them so they do not leak. Or, you can use a pooled set of connections where they are automatically returned to the pool after doing a query.