Node.js Practical Debugging — Express listen (Async Bug). The code logs undefined, returns before data arrives, or silently loses an error. Fix the asynchronous flow using async/await or proper promise handling. The specific area is wrong port, env port and server binding issues. Assume a real Express/Node.js project where the developer needs a reliable, maintainable fix. Explain why the buggy version can fail, then provide corrected code and the expected behavior. Do not hide the root cause behind a generic 'restart the server' answer.
BUGGY/PROBLEM CODE:
const express = require('express');
const router = express.Router();
router.get('/users/:id', async (req, res) => {
const user = await getUser(req.params.userID);
res.json(user);
});
app.use('/api', router);
TASK: Find the exact problem and write the production-safe correction.
Looking for the latest
Sarkari Result 2026
updates?
Check the latest government exam
results, merit lists and result updates
on Sarkari Resultess.
यह option जानबूझकर एक common bug/unsafe approach दिखाता है। इसे production solution के रूप में इस्तेमाल करने से पहले variable scope, async flow, module path, validation, error handling और security checks verify करें। ऊपर दिए गए correct option से exact difference compare करें.
Verified
Correct Answer
Correct Code / Solution
const express = require('express');
const router = express.Router();
router.get('/users/:id', async (req, res, next) => {
try {
const user = await getUser(req.params.id);
if (!user) return res.status(404).json({success:false, message:'User not found'});
return res.json({success:true, data:user});
} catch (error) {
return next(error);
}
});
app.use('/api', router); // final URL: GET /api/users/:id
Additional Explanation
Root cause: wrong port, env port and server binding issues. The important debugging step is to verify the exact runtime value, module path, middleware order, environment variable, database/model export, or asynchronous result before changing unrelated code. The corrected version adds explicit validation/error handling where appropriate.
Expected behavior: the code should either complete the requested operation or return/log a controlled error instead of failing silently, returning undefined unexpectedly, or crashing the process.
Verified
Possible but Incorrect Code
const express = require('express');
const router = express.Router();
router.get('/users/:id', async (req, res, next) => {
try {
const user = getUser(req.params.id);
if (!user) return res.status(404).json({success:false, message:'User not found'});
return res.json({success:true, data:user});
} catch (error) {
return next(error);
}
});
app.use('/api', router); // final URL: GET /api/users/:id
Additional Explanation
यह option जानबूझकर एक common bug/unsafe approach दिखाता है। इसे production solution के रूप में इस्तेमाल करने से पहले variable scope, async flow, module path, validation, error handling और security checks verify करें। ऊपर दिए गए correct option से exact difference compare करें.
यह option जानबूझकर एक common bug/unsafe approach दिखाता है। इसे production solution के रूप में इस्तेमाल करने से पहले variable scope, async flow, module path, validation, error handling और security checks verify करें। ऊपर दिए गए correct option से exact difference compare करें.