API versioning strategies in Express - Mini Project: Build & Apply

API Versioning Strategies with Express

📖 Scenario: You are building a simple web API for a bookstore. Over time, you want to support different versions of the API so clients can choose which version to use without breaking their apps.

🎯 Goal: Create an Express server that supports two API versions: v1 and v2. Each version should have a route /books that returns a different message indicating the version.

📋 What You'll Learn

Create an Express app with a basic route for version 1 at /api/v1/books

Add a configuration variable to hold the current API version

Create a route for version 2 at /api/v2/books that returns a different message

Set up the Express app to listen on port 3000

💡 Why This Matters

🌍 Real World

APIs often need to support multiple versions so that old clients keep working while new features are added.

💼 Career

Understanding API versioning is important for backend developers working with web services and maintaining backward compatibility.

1

Set up Express and create the version 1 route

Create an Express app by requiring express and calling express(). Then create a GET route at /api/v1/books that sends the text 'Books API Version 1' as the response.

Express

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

// Your code here

Hint

Use require('express') to import Express and express() to create the app. Then use app.get to define the route.

2

Add a configuration variable for the current API version

Create a constant variable called currentVersion and set it to the string 'v2' to represent the current API version.

Express

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

app.get('/api/v1/books', (req, res) => {
  res.send('Books API Version 1');
});

// Your code here

Hint

Use const currentVersion = 'v2' to store the current API version.

3

Create the version 2 route with a different response

Add a GET route at /api/v2/books that sends the text 'Books API Version 2' as the response.

Express

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

app.get('/api/v1/books', (req, res) => {
  res.send('Books API Version 1');
});

const currentVersion = 'v2';

// Your code here

Hint

Use app.get with the path /api/v2/books and send the correct response text.

4

Start the Express server on port 3000

Add code to make the Express app listen on port 3000 and log the message 'Server running on port 3000' when it starts.

Express

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

app.get('/api/v1/books', (req, res) => {
  res.send('Books API Version 1');
});

const currentVersion = 'v2';

app.get('/api/v2/books', (req, res) => {
  res.send('Books API Version 2');
});

// Your code here

Hint

Use app.listen(3000, () => { console.log('Server running on port 3000') }) to start the server.

Practice

1. Which of the following is a common method to implement API versioning in Express?

easy

A. Using the URL path to specify the version, like /v1/users

B. Changing the database schema for each version

C. Using different port numbers for each API version

D. Renaming the Express app for each version

Solution

1. Step 1: Understand common API versioning methods

   API versioning often uses the URL path, headers, or query parameters to distinguish versions.

2. Step 2: Identify the correct method in Express

   Using the URL path like /v1/users is a standard and clear way to version APIs in Express.

3. Final Answer:

   Using the URL path to specify the version, like /v1/users -> Option A

4. Quick Check:

   URL path versioning = Using the URL path to specify the version, like /v1/users [OK]

Hint: API versions often appear in the URL path [OK]

Common Mistakes:

• Thinking database changes are API versioning
• Using different ports instead of URL or headers
• Renaming the app does not affect API versioning

2. Which Express code snippet correctly sets up API versioning using URL path?

easy

A. app.get('v1/users', userRouter);

B. app.use('/v1/users', userRouter);

C. app.route('/users/v1').get(userRouter);

D. app.listen('/v1/users', userRouter);

Solution

1. Step 1: Review Express routing syntax

   Express uses app.use(path, router) to mount routers on paths.

2. Step 2: Identify correct versioning path usage

   Using app.use('/v1/users', userRouter); correctly mounts the router for version 1 users.

3. Final Answer:

   app.use('/v1/users', userRouter); -> Option B

4. Quick Check:

   Correct Express routing = app.use('/v1/users', userRouter); [OK]

Hint: Use app.use with path and router for versioning [OK]

Common Mistakes:

• Missing leading slash in path
• Using app.get instead of app.use for routers
• Incorrect method like app.listen for routing

3. Given this Express code, what is the response when a client requests /api/users?

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

app.use('/api/v1/users', (req, res) => res.send('Version 1 users'));
app.use('/api/v2/users', (req, res) => res.send('Version 2 users'));

app.listen(3000);

medium

A. Cannot GET /api/users

B. Version 2 users

C. Version 1 users

D. Server error

Solution

1. Step 1: Check defined routes

   Routes are defined only for /api/v1/users and /api/v2/users.

2. Step 2: Analyze request path

   The request is for /api/users, which does not match any defined route.

3. Final Answer:

   Cannot GET /api/users -> Option A

4. Quick Check:

   Undefined route returns 404 = Cannot GET /api/users [OK]

Hint: Check exact route paths before guessing response [OK]

Common Mistakes:

• Assuming /api/users matches /api/v1/users
• Expecting default route without defining it
• Confusing middleware with route handlers

4. Identify the error in this Express API versioning code:

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

app.use('/v1/users', userRouter);
app.use('/v2/users', userRouter);

app.listen(3000);

Assuming userRouter handles all user routes.

medium

A. Both versions use the same router instance, causing version conflicts

B. Missing const before userRouter

C. Routes should use app.get instead of app.use

D. No error; this is a valid versioning setup

Solution

1. Step 1: Understand router reuse in Express

   Using the same router instance for different paths is valid and common in Express.

2. Step 2: Check for syntax and method correctness

   Using app.use to mount routers on different paths is correct; no syntax errors present.

3. Final Answer:

   No error; this is a valid versioning setup -> Option D

4. Quick Check:

   Router reuse with different paths is valid = No error; this is a valid versioning setup [OK]

Hint: Reusing routers for versions is allowed in Express [OK]

Common Mistakes:

• Thinking router reuse causes conflicts
• Confusing app.use with app.get for routers
• Expecting separate router instances per version

5. You want to support API versioning in Express using request headers instead of URL paths. Which code snippet correctly reads the version from the header X-API-Version and routes accordingly?

hard

A. app.use('/v1/users', userRouter);
app.use('/v2/users', userV2Router);

B. app.use('/users', (req, res) => {
const version = req.query.version;
if (version === '1') userRouter(req, res);
else userV2Router(req, res);
});

C. app.use((req, res, next) => {
const version = req.headers['x-api-version'];
if (version === '1') userRouter(req, res, next);
else if (version === '2') userV2Router(req, res, next);
else res.status(400).send('Invalid API version');
});

D. app.get('/users', (req, res) => {
const version = req.headers['api-version'];
if (version === '1') res.send('User v1');
else res.send('User v2');
});

Solution

1. Step 1: Identify header-based versioning approach

   Version is read from X-API-Version header in the request.

2. Step 2: Check routing logic based on header

   app.use((req, res, next) => { const version = req.headers['x-api-version']; if (version === '1') userRouter(req, res, next); else if (version === '2') userV2Router(req, res, next); else res.status(400).send('Invalid API version'); }); reads the header, then calls the correct router or returns error if invalid.

3. Final Answer:

   app.use((req, res, next) => { const version = req.headers['x-api-version']; if (version === '1') userRouter(req, res, next); else if (version === '2') userV2Router(req, res, next); else res.status(400).send('Invalid API version'); }); -> Option C

4. Quick Check:

   Header-based routing = app.use((req, res, next) => { const version = req.headers['x-api-version']; if (version === '1') userRouter(req, res, next); else if (version === '2') userV2Router(req, res, next); else res.status(400).send('Invalid API version'); }); [OK]

Hint: Use middleware to check headers and route accordingly [OK]

Common Mistakes:

• Using query parameters instead of headers
• Not calling next() or router properly
• Checking wrong header name