How do you version an API? | API Interview Questions

What You'll Learn

Why version APIs
Versioning strategies
Best practices

Why Version?

Make breaking changes without breaking clients
Support multiple versions simultaneously
Gradual migration path

Versioning Strategies

1. URL Path (Most Common)

code.jsJavaScript

GET /api/v1/users
GET /api/v2/users

2. Query Parameter

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GET /api/users?version=1
GET /api/users?version=2

3. Header

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GET /api/users
Accept: application/vnd.api+json;version=1

4. Content Negotiation

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GET /api/users
Accept: application/vnd.company.v1+json

Implementation Example

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// Express.js with URL versioning
const express = require('express');
const app = express();

// Version 1
app.use('/api/v1', require('./routes/v1'));

// Version 2
app.use('/api/v2', require('./routes/v2'));

// Or with a router
const v1Router = express.Router();
v1Router.get('/users', (req, res) => {
  res.json({ version: 1, data: users });
});

Best Practices

Use URL path versioning for simplicity
Support at least 2 versions
Deprecate old versions with notice
Document breaking changes