Controllers

Controllers are responsible for handling incoming requests and returning responses to the client.

Defining Controllers

A controller is a class decorated with @Controller(). The decorator accepts a path prefix that will be prepended to all routes defined in the controller.

import { Controller, Get, Post, pathParam, response } from '@zeltjs/core';
import { validated } from '@zeltjs/validator-valibot';
import * as v from 'valibot';

const CreateUserBody = v.object({
  name: v.string(),
  email: v.pipe(v.string(), v.email()),
});

@Controller('/users')
export class UserController {
  @Get('/')
  findAll() {
    return { users: [] };
  }

  @Get('/:id')
  findOne(id = pathParam('id')) {
    return { id, name: 'John Doe' };
  }

  @Post('/')
  create(body = validated(CreateUserBody), res = response()) {
    return res.json({ id: '1', ...body }, 201);
  }
}

Route Path Rules

The @Controller prefix and method decorator path are joined to form the final route. Trailing slashes are stripped; leading slashes on the method path are optional.

Controller Prefix	Method Path	Final Route
'/users'	'/'	/users
'/users'	'/:id'	/users/:id
'/api'	'/users'	/api/users
'/'	'/hello'	/hello
'/api/v1'	'/users/:id'	/api/v1/users/:id

tip

Both @Get('/items') and @Get('items') produce the same result — a leading slash is added automatically if missing.

HTTP Method Decorators

Zelt provides decorators for all standard HTTP methods:

Decorator	HTTP Method
@Get()	GET
@Post()	POST
@Put()	PUT
@Patch()	PATCH
@Delete()	DELETE

@Controller('/items')
export class ItemController {
  @Get('/')
  findAll() { /* ... */ }

  @Get('/:id')
  findOne(id = pathParam('id')) { /* ... */ }

  @Post('/')
  create(body = validated(schema)) { /* ... */ }

  @Put('/:id')
  update(id = pathParam('id'), body = validated(schema)) { /* ... */ }

  @Patch('/:id')
  patch(id = pathParam('id'), body = validated(schema)) { /* ... */ }

  @Delete('/:id')
  remove(id = pathParam('id')) { /* ... */ }
}

Route Parameters

Use pathParam() to extract route parameters:

@Controller('/items')
class ItemController {
  @Get('/:category/:id')
  findOne(
    category = pathParam('category'),
    id = pathParam('id')
  ) {
    return { category, id };
  }
}

Request Body

With Validation (Recommended)

Use validated() with a Valibot schema to validate and type the request body:

const CreatePostBody = v.object({
  title: v.pipe(v.string(), v.minLength(1), v.maxLength(100)),
  content: v.string(),
  tags: v.optional(v.array(v.string())),
});

@Controller('/posts')
class PostController {
  @Post('/')
  create(body = validated(CreatePostBody)) {
    // body is fully typed as { title: string; content: string; tags?: string[] }
    return { id: '1', ...body };
  }
}

If validation fails, Zelt automatically returns a 400 response with detailed error information.

Without Validation

For cases where you don't need validation (e.g., accepting arbitrary JSON), use the body() primitive:

@Controller('/webhooks')
class WebhookController {
  @Post('/github')
  handleGithubWebhook(payload = body()) {
    // payload is typed as unknown
    return { received: true };
  }
}

See Request & Response Primitives for more details on body() and other request helpers.

Returning Responses

Controller methods support two return styles:

Plain Return (Recommended for 200 OK)

Simply return a value — Zelt automatically serializes it as JSON with status 200:

@Controller('/users')
class UserController {
  @Get('/')
  findAll() {
    return { users: [] }; // → 200 OK, Content-Type: application/json
  }

  @Get('/health')
  health() {
    return 'OK'; // → 200 OK, Content-Type: text/plain
  }
}

response() (For Custom Status Codes or Headers)

Use response() when you need a status code other than 200, custom headers, or redirects:

@Controller('/users')
class UserController {
  @Post('/')
  create(body = validated(schema), res = response()) {
    return res.json({ id: '1', ...body }, 201); // 201 Created
  }

  @Delete('/:id')
  remove(id = pathParam('id')) {
    return new Response(null, { status: 204 }); // 204 No Content
  }
}

When to Use Which

Scenario	Approach
Return JSON with 200	return { data }
Return with custom status (201, 204, etc.)	response().json(data, status)
Set custom headers	response().header(name, value).json(data)
Redirect	response().redirect(url)
Set cookies	response().setCookie(name, value).json(data)
Stream response	response().stream(cb) / response().sse(cb)

See Request & Response Primitives for the full response() API.

Custom Response Status

Use response() to control the HTTP status code:

@Controller('/items')
class ItemController {
  @Post('/')
  create(body = validated(schema), res = response()) {
    const created = { id: '1', ...body };
    return res.json(created, 201); // Returns 201 Created
  }

  @Delete('/:id')
  remove(id = pathParam('id')) {
    // Perform delete operation
    return new Response(null, { status: 204 }); // Returns 204 No Content
  }
}

Registering Controllers

Controllers must be registered in createApp():

export const app = createApp([http({
    controllers: [UserController, PostController],
  })]);

Next Steps

• Learn about Middleware for request/response processing