**Course Title:** Mastering Express.js: Building Scalable Web Applications and APIs **Section Title:** Building RESTful APIs **Topic:** Implementing versioning for APIs API versioning is a crucial aspect of maintaining a scalable and maintainable RESTful API. As your API evolves, you'll inevitably need to make changes to endpoints, request parameters, or response formats. Implementing versioning helps ensure that your API remains backward compatible and prevents breaking changes from affecting existing clients. **Why API Versioning is Important** API versioning is essential for several reasons: 1. **Backward compatibility**: By maintaining multiple versions of your API, you can ensure that existing clients continue to work even when you make changes to the API. 2. **Flexibility**: Versioning allows you to experiment with new features and API endpoints without affecting existing clients. 3. **Decoupling**: Versioning helps decouple your API from specific client implementations, making it easier to upgrade or change the API without affecting clients. **API Versioning Strategies** There are several API versioning strategies you can use, including: ### 1. URI Versioning In this approach, the version number is included in the URI of the API endpoint. For example: ```bash https://api.example.com/v1/users https://api.example.com/v2/users ``` **Example implementation in Express.js:** ```javascript const express = require('express'); const app = express(); // URI versioning app.use('/v1', require('./v1/routes')); app.use('/v2', require('./v2/routes')); ``` ### 2. Query Parameter Versioning In this approach, the version number is passed as a query parameter in the URL. For example: ```bash https://api.example.com/users?version=1 https://api.example.com/users?version=2 ``` **Example implementation in Express.js:** ```javascript const express = require('express'); const app = express(); // Query parameter versioning app.get('/users', (req, res) => { const version = req.query.version; if (version === '1') { // Handle v1 request } else if (version === '2') { // Handle v2 request } }); ``` ### 3. Media Type Versioning In this approach, the version number is included in the `Accept` header of the HTTP request. For example: ```bash GET /users HTTP/1.1 Accept: application/vnd.example.v1+json ``` **Example implementation in Express.js:** ```javascript const express = require('express'); const app = express(); // Media type versioning app.get('/users', (req, res) => { const acceptHeader = req.headers.accept; if (acceptHeader.includes('vnd.example.v1+json')) { // Handle v1 request } else if (acceptHeader.includes('vnd.example.v2+json')) { // Handle v2 request } }); ``` ### 4. Header Versioning In this approach, the version number is included in a custom header of the HTTP request. For example: ```bash GET /users HTTP/1.1 X-API-Version: 1 ``` **Example implementation in Express.js:** ```javascript const express = require('express'); const app = express(); // Header versioning app.get('/users', (req, res) => { const versionHeader = req.headers['x-api-version']; if (versionHeader === '1') { // Handle v1 request } else if (versionHeader === '2') { // Handle v2 request } }); ``` **Best Practices for API Versioning** When implementing API versioning, keep the following best practices in mind: 1. **Use a consistent versioning strategy**: Choose a versioning strategy and stick to it throughout your API. 2. **Document your API versions**: Clearly document the different versions of your API, including the changes and deprecations in each version. 3. **Provide a deprecated notice**: When deprecating an API version, provide a clear notice to clients about the deprecation and the timeline for removal. 4. **Test your API versions**: Thoroughly test each version of your API to ensure that it works as expected. **Conclusion** API versioning is a critical aspect of maintaining a scalable and maintainable RESTful API. By understanding the different versioning strategies and implementing a consistent versioning approach, you can ensure that your API remains backward compatible and flexible. Remember to follow best practices for API versioning to ensure a smooth transition between versions. **Practice Exercise:** Implement URI versioning in an Express.js API using the following requirements: * Create two API endpoints, `/v1/users` and `/v2/users`, that return different responses. * Test the API using a tool like Postman or `curl`. **External Resources:** * [API Versioning](https://segment.com/blog/api-versioning) by Segment * [API Versioning Strategies](https://blog.restcase.com/api-versioning-strategies) by RestCase **Leave a comment below if you have any questions or need help with implementing API versioning in your Express.js API.**

https://api.example.com/v1/users
https://api.example.com/v2/users

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

// URI versioning
app.use('/v1', require('./v1/routes'));
app.use('/v2', require('./v2/routes'));

https://api.example.com/users?version=1
https://api.example.com/users?version=2

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

// Query parameter versioning
app.get('/users', (req, res) => {
  const version = req.query.version;
  if (version === '1') {
    // Handle v1 request
  } else if (version === '2') {
    // Handle v2 request
  }
});

GET /users HTTP/1.1
Accept: application/vnd.example.v1+json

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

// Media type versioning
app.get('/users', (req, res) => {
  const acceptHeader = req.headers.accept;
  if (acceptHeader.includes('vnd.example.v1+json')) {
    // Handle v1 request
  } else if (acceptHeader.includes('vnd.example.v2+json')) {
    // Handle v2 request
  }
});

GET /users HTTP/1.1
X-API-Version: 1

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

// Header versioning
app.get('/users', (req, res) => {
  const versionHeader = req.headers['x-api-version'];
  if (versionHeader === '1') {
    // Handle v1 request
  } else if (versionHeader === '2') {
    // Handle v2 request
  }
});