Hypermedia as the Engine of Application State, or HATEOAS, is a key idea in contemporary API design that improves RESTful APIs by making them more discoverable and self-descriptive. Instead of depending on hardcoded endpoints, it enables clients to dynamically explore an API through hypermedia links.

In this article, we’ll explore:

✅ What HATEOAS is and why it matters.
✅ How it improves API usability.
✅ A practical implementation using Node.js and Express.

What is HATEOAS?

HATEOAS is a limitation of RESTful API architecture, in which hyperlinks included in answers allow a client to communicate with a server. The client follows links that are presented dynamically rather than knowing all potential API endpoints beforehand.

Example Without HATEOAS (Traditional API Response)

{
  "id": 1,
  "name": "John Doe",
  "email": "john@example.com"
}

The client must already know where to send requests to update or delete the user.

Example With HATEOAS (Hypermedia Links)

{
  "id": 1,
  "name": "John Doe",
  "email": "john@example.com",
  "_links": {
    "self": { "href": "/users/1" },
    "update": { "href": "/users/1", "method": "PUT" },
    "delete": { "href": "/users/1", "method": "DELETE" }
  }
}

Here, the response guides the client on how to interact with the resource.

Why Use HATEOAS?

Implementing HATEOAS in a Node.js API

Let’s build a simple REST API with HATEOAS using Node.js and Express.

Step 1: Install Dependencies

npm init -y
npm install express

Step 2: Set Up Express Server

import express from "express";

const app = express();
const port = 3000;

app.use(express.json());

// Sample Users
const users = [
  { id: 1, name: "John Doe", email: "john@example.com" },
  { id: 2, name: "Jane Smith", email: "jane@example.com" }
];

// Helper function to generate HATEOAS links
const generateUserLinks = (userId: number) => ({
  self: { href: `/users/${userId}` },
  update: { href: `/users/${userId}`, method: "PUT" },
  delete: { href: `/users/${userId}`, method: "DELETE" }
});

// GET all users
app.get("/users", (req, res) => {
  const response = users.map(user => ({
    ...user,
    _links: generateUserLinks(user.id)
  }));
  res.json(response);
});

// GET a single user with HATEOAS links
app.get("/users/:id", (req, res) => {
  const user = users.find(u => u.id === parseInt(req.params.id));
  if (!user) return res.status(404).json({ error: "User not found" });

  res.json({ ...user, _links: generateUserLinks(user.id) });
});

app.listen(port, () => console.log(`Server running on http://localhost:${port}`));

Testing the API

Run the server:

node index.js

Retrieve Users:

GET /users

Response:

[
  {
    "id": 1,
    "name": "John Doe",
    "email": "john@example.com",
    "_links": {
      "self": { "href": "/users/1" },
      "update": { "href": "/users/1", "method": "PUT" },
      "delete": { "href": "/users/1", "method": "DELETE" }
    }
  }
]

The client can follow these links dynamically instead of hardcoding API paths.

When to Use HATEOAS?

Conclusion

HATEOAS makes APIs more flexible and self-explanatory, which enhances their usefulness. Clients can now follow hypermedia URLs instead of hardcoding API paths. In large APIs and microservices, it improves scalability, flexibility, and maintainability although adding some complexity.

Key Takeaways:

→ HATEOAS enables hypermedia-driven RESTful APIs.
→ Clients discover endpoints dynamically through embedded links.
→ Best suited for public APIs and microservices.
→ Adds flexibility, but comes with performance trade-offs.

By implementing HATEOAS, you’re one step closer to truly RESTful API design!