1. Introduction

Goal of the Tutorial

This tutorial aims to teach you how to implement versioning in your API and how to effectively document it.

Learning Outcomes

By the end of this tutorial, you will understand the significance of API versioning, the different strategies to version your API, and how to document your API using tools such as Swagger.

Prerequisites

• Basic knowledge of APIs (Application Programming Interfaces)
• Familiarity with a programming language (We'll use JavaScript in this tutorial)
• Basic understanding of JSON (JavaScript Object Notation)

2. Step-by-Step Guide

API versioning allows developers to introduce non-breaking changes to their APIs without affecting the existing end-users. There are three common strategies for versioning APIs: URI versioning, request header versioning, and parameter versioning.

Documenting your API is crucial to ensure it's easily understandable and usable by other developers. Swagger is a popular tool for API documentation due to its user-friendly interface and support for JSON and XML.

URI Versioning

This is the most straightforward approach where the version number is included in the URL.

// Version 1
app.get('/v1/users', function(req, res) { ... });

// Version 2
app.get('/v2/users', function(req, res) { ... });

Request Header Versioning

In this approach, the version number is sent in the request header.

app.get('/users', function(req, res) {
  var version = req.headers['version'];
  if(version == 'v1') { ... }
  else if(version == 'v2') { ... }
});

Parameter Versioning

Here, the version number is sent as a query parameter in the request.

app.get('/users', function(req, res) {
  var version = req.query.version;
  if(version == 'v1') { ... }
  else if(version == 'v2') { ... }
});

3. Code Examples

Let's look at a practical example of versioning and documenting an API with Swagger.

API Versioning with Express.js

We'll use URI versioning in this example. We have two versions of our 'users' endpoint.

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

// Version 1
app.get('/v1/users', function(req, res) {
  res.json({ msg: 'Welcome to version 1 of our API' });
});

// Version 2
app.get('/v2/users', function(req, res) {
  res.json({ msg: 'Welcome to version 2 of our API' });
});

app.listen(3000, function() {
  console.log('App listening on port 3000');
});

API Documentation with Swagger

First, install Swagger:

npm install swagger-ui-express swagger-jsdoc

Then, set up Swagger in your app:

const swaggerJsDoc = require('swagger-jsdoc');
const swaggerUi = require('swagger-ui-express');

const swaggerOptions = {
  definition: {
    openapi: "3.0.0",
    info: {
      title: "My API",
      version: "1.0.0",
    },
  },
  apis: ["app.js"],
};

const swaggerDocs = swaggerJsDoc(swaggerOptions);
app.use("/api-docs", swaggerUi.serve, swaggerUi.setup(swaggerDocs));

4. Summary

We've covered API versioning strategies including URI versioning, request header versioning, and parameter versioning. We've also discussed how to document your API using Swagger.

5. Practice Exercises

1. Implement versioning for another endpoint in our Express.js app.
2. Document the new endpoint using Swagger.
3. Try out different versioning strategies and observe the differences.

Remember, practice is key in mastering any new concept. Continue to use these strategies in your future API projects.