API versioning strategies in Express - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is API versioning and why is it important?

API versioning is a way to manage changes in an API over time. It helps keep old clients working while allowing new features or fixes in newer versions. This avoids breaking existing apps when the API changes.

beginner

Name three common API versioning strategies used in Express apps.

1. URI versioning (e.g., /v1/users)
2. Query parameter versioning (e.g., /users?version=1)
3. Header versioning (using custom headers like 'Accept-Version')

beginner

How does URI versioning work in Express?

URI versioning adds the version number directly in the URL path. For example, '/v1/users' and '/v2/users' are two versions. Express routes are set up to handle each version separately.

intermediate

What is a benefit of using header versioning over URI versioning?

Header versioning keeps URLs clean and consistent. Clients specify the version in HTTP headers, so the URL stays the same. This can be better for caching and hides version details from the URL.

beginner

Show a simple Express route example using URI versioning for version 1 and version 2.

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

app.get('/v1/users', (req, res) => {
  res.send('Users from API version 1');
});

app.get('/v2/users', (req, res) => {
  res.send('Users from API version 2 with new data');
});

app.listen(3000);

Which of these is NOT a common API versioning strategy?

A Header versioning

B Query parameter versioning

C Database versioning

D URI versioning

Database versioning is unrelated to API versioning strategies. The others are common ways to version APIs.

In URI versioning, where is the version number placed?

A In the URL path

B In the request body

C In the query string

D In the HTTP header

URI versioning places the version number directly in the URL path, like '/v1/resource'.

What is a key advantage of header versioning?

A Simplifies URL structure

B Makes URLs longer

C Requires no headers

D Breaks caching

Header versioning keeps URLs clean and simple by moving version info to headers.

Which Express method is used to define a route for a specific API version?

A app.listen()

B app.get()

C app.version()

D app.routeVersion()

app.get() defines a GET route; versioning is handled by the URL or headers, not a special method.

Why is API versioning important when updating an API?

A To avoid using HTTP headers

B To break old clients intentionally

C To make URLs longer

D To allow new features without breaking existing clients

Versioning lets you add features or fix bugs without breaking apps that use older API versions.

Explain the differences between URI versioning, query parameter versioning, and header versioning in APIs.

Think about where the version info is placed and how clients specify it.

Describe how you would implement API versioning in an Express app using URI versioning.

Focus on route setup and handling different versions.

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