API versioning strategies in Express - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding URL Path Versioning

In Express.js, what is the main advantage of using URL path versioning like /api/v1/resource for API versioning?

A It automatically updates the API version without changing client requests.

B It hides the API version from clients to simplify URLs.

C It allows clients to specify the API version in the URL, making it easy to route requests to different handlers.

D It forces all clients to use the latest API version only.

💡 Hint

Think about how the server knows which version of the API to use based on the request URL.

URL path versioning explicitly includes the version in the URL, so the server can easily route requests to the correct version handler. This makes version management clear and straightforward.

❓ component_behavior

intermediate

Header Versioning Behavior

Given an Express.js API that uses a custom header X-API-Version to determine the API version, what happens if a client sends a request without this header?

Express

app.use((req, res, next) => {
  const version = req.headers['x-api-version'] || '1';
  if(version === '1') {
    // handle v1
    res.send('Response from API v1');
  } else if(version === '2') {
    // handle v2
    res.send('Response from API v2');
  } else {
    res.status(400).send('Unsupported API version');
  }
});

A The server responds with 'Response from API v2' by default.

B The server responds with 'Response from API v1' because it defaults to version 1.

C The server crashes due to missing header.

D The server responds with 'Unsupported API version' error.

💡 Hint

Look at how the version variable is assigned when the header is missing.

The code uses a default value of '1' if the X-API-Version header is missing, so it responds with the v1 handler.

📝 Syntax

advanced

Middleware Version Routing Syntax

Which Express.js middleware setup correctly routes requests to different API versions using URL path versioning?

Express

const express = require('express');
const app = express();

// Version 1 handler
const v1Router = express.Router();
v1Router.get('/users', (req, res) => res.send('Users from v1'));

// Version 2 handler
const v2Router = express.Router();
v2Router.get('/users', (req, res) => res.send('Users from v2'));

// Mount routers here
// ???

app.listen(3000);

A

app.use('/api/v1', v1Router);
app.use('/api/v2', v2Router);

B

app.use('/v1/api', v1Router);
app.use('/v2/api', v2Router);

C

app.use('/api', v1Router);
app.use('/api', v2Router);

D

app.use(v1Router);
app.use(v2Router);

💡 Hint

Think about how the URL path should include the version segment before the resource path.

Mounting the routers on /api/v1 and /api/v2 correctly separates the versions in the URL path, allowing Express to route requests properly.

🔧 Debug

advanced

Debugging Query Parameter Versioning

Consider this Express.js code snippet that tries to version an API using a query parameter ?version=2. What is the bug causing all requests to respond with 'Version 2 response' regardless of the query parameter?

Express

app.get('/api/users', (req, res) => {
  const version = req.query.version;
  if(version === '2') {
    res.send('Version 2 response');
  } else {
    res.send('Version 1 response');
  }
});

A The route path should include the version like /api/v2/users.

B The query parameter should be accessed as req.params.version, not req.query.version.

C The res.send calls are missing return statements.

D The code uses assignment (=) instead of comparison (===) in the if condition.

💡 Hint

Check the if condition syntax carefully.

The condition if(version = '2') assigns '2' to version instead of comparing it, so it always evaluates to true, causing the else block to never run.

❓ state_output

expert

Output of Combined Versioning Middleware

What is the output when a client sends a GET request to /api/users with header X-API-Version: 2 given this Express.js code?

Express

const express = require('express');
const app = express();

app.use('/api', (req, res, next) => {
  req.apiVersion = req.headers['x-api-version'] || '1';
  next();
});

app.get('/api/users', (req, res) => {
  switch(req.apiVersion) {
    case '1':
      res.send('Users from API v1');
      break;
    case '2':
      res.send('Users from API v2');
      break;
    default:
      res.status(400).send('Unsupported API version');
  }
});

app.listen(3000);

A Users from API v2

B Users from API v1

C Unsupported API version

D Error: Cannot read property 'apiVersion' of undefined

💡 Hint

Look at how the middleware sets req.apiVersion and how the route uses it.

The middleware sets req.apiVersion from the header or defaults to '1'. The route reads this value and sends the matching response. Since the header is '2', it sends 'Users from API v2'.