HATEOAS: Hypermedia Links in API Responses

API clients hardcode URL construction logic (string concatenation for resource URLs). When URL patterns change, all clients break simultaneously.

Include hypermedia links in responses so clients discover navigation from the API itself.

// Response includes links to related actions
app.get('/users/:id', async (req, res) => {
  const user = await db.getUser(req.params.id);
  const baseUrl = `${req.protocol}://${req.get('host')}`;

  res.json({
    id: user.id,
    name: user.name,
    email: user.email,
    _links: {
      self: { href: `${baseUrl}/users/${user.id}`, method: 'GET' },
      update: { href: `${baseUrl}/users/${user.id}`, method: 'PUT' },
      delete: { href: `${baseUrl}/users/${user.id}`, method: 'DELETE' },
      orders: { href: `${baseUrl}/users/${user.id}/orders`, method: 'GET' },
    },
  });
});

// Collection response with pagination links
app.get('/users', async (req, res) => {
  const { users, nextCursor } = await db.getUsers();
  res.json({
    items: users,
    _links: {
      self: { href: `${baseUrl}/users` },
      next: nextCursor
        ? { href: `${baseUrl}/users?cursor=${nextCursor}` }
        : null,
    },
  });
});

HATEOAS (Hypermedia as the Engine of Application State) makes APIs self-describing. Clients navigate by following links rather than constructing URLs, decoupling them from URL structure.