Health check endpoints in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this simple health check endpoint?

Consider this Node.js Express health check endpoint. What response does the server send when a GET request is made to /health?

Node.js

import express from 'express';
const app = express();
app.get('/health', (req, res) => {
  res.status(200).json({ status: 'ok' });
});
// Assume server listens correctly

A {"status":"ok"}

B Status code 404 with empty body

C Status code 500 with error message

D Plain text response 'ok' with status 200

💡 Hint

Look at the response method used and the status code set.

The endpoint sends a JSON response with status code 200 and body {"status":"ok"}.

📝 Syntax

intermediate

Which option causes a syntax error in this health check endpoint?

Identify which code snippet will cause a syntax error when defining a health check endpoint in Express.

A app.get('/health', (req, res) => { res.status(200).json({ status: 'ok' ) }); });

B app.get('/health', (req, res) => res.json({ status: 'ok' }));

C app.get('/health', (req, res) => { res.send('OK'); });

D app.get('/health', function(req, res) { res.sendStatus(200); });

💡 Hint

Look carefully at the brackets and parentheses in the JSON response.

Option A has a mismatched parenthesis in json({ status: 'ok' ) causing a syntax error.

❓ state_output

advanced

What is the output when the health check endpoint uses async function but forgets to await?

Given this health check endpoint, what will the client receive when requesting /health?

Node.js

app.get('/health', async (req, res) => {
  const status = checkDatabase(); // async function returning a promise
  res.json({ dbStatus: status });
});

async function checkDatabase() {
  return 'connected';
}

A Empty JSON object {}

B {"dbStatus":"connected"}

C Status code 500 with error

D {"dbStatus":{}}

💡 Hint

Remember what happens if you don't await a promise before sending it in JSON.

The status variable is a Promise object because checkDatabase() is async and not awaited. Sending it directly serializes the Promise object, not its resolved value.

🔧 Debug

advanced

Why does this health check endpoint cause the server to hang?

Examine this health check endpoint code. Why does the server never respond to requests on /health?

Node.js

app.get('/health', (req, res) => {
  checkServiceStatus();
});

function checkServiceStatus() {
  // some async operation but no callback or promise handling
  setTimeout(() => {
    console.log('Service is up');
  }, 1000);
}

A The console.log throws an error stopping the response.

B The setTimeout blocks the event loop causing the hang.

C The endpoint never calls res.send or res.json, so the client waits forever.

D The endpoint returns a promise but does not handle rejection.

💡 Hint

Think about what the server must do to finish a request.

The endpoint calls an async function but never sends a response. The client waits indefinitely.

🧠 Conceptual

expert

Which option best describes the purpose of a health check endpoint in a Node.js service?

Choose the most accurate description of why health check endpoints are used in backend services.

A To authenticate users before allowing access to the main application.

B To provide a simple URL that external systems can call to verify the service is running and responsive.

C To expose detailed internal metrics and logs for debugging purposes.

D To serve the main content of the application to users.

💡 Hint

Think about monitoring and uptime checks.

Health check endpoints are lightweight URLs used by monitoring tools to confirm the service is alive and responsive.