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Version: 13.x

Getting started

This guide creates a small versioned API with one controller and a validated endpoint.

Requirements​

  • Node.js 22 or newer
  • A TypeScript project using CommonJS-compatible output
  • experimentalDecorators and emitDecoratorMetadata enabled

Install Amala​

Add Amala to an existing project:

npm install amala

Or generate a starter application:

npm create amala-app@latest my-api

The rest of this guide shows the manual setup so each moving part is visible.

Configure TypeScript​

Use this as a baseline tsconfig.json:

{
  "compilerOptions": {
    "emitDecoratorMetadata": true,
    "esModuleInterop": true,
    "experimentalDecorators": true,
    "module": "commonjs",
    "outDir": "dist",
    "skipLibCheck": true,
    "strict": true,
    "target": "ES2022"
  },
  "include": ["src/**/*.ts"]
}

Both decorator settings are required. Without emitted type metadata, Amala cannot transform and validate class-based handler arguments.

These settings select TypeScript's legacy decorator implementation. Standard decorators do not currently support parameter decorators such as @Body() or automatically emit the parameter types Amala needs.

Create and bootstrap the app​

Start with the controller, then open the main.ts tab to see how it becomes a running application:

import {Controller, Get} from 'amala';

@Controller('/health')
export class HealthController {
  @Get('/')
  status() {
    return {status: 'ok'};
  }
}

Compile and run the application with the scripts used by your project. Request:

GET http://localhost:3000/api/v1/health

The response is:

{"status":"ok"}

Version v1 is enabled by default. To serve GET /api/health, set disableVersioning: true. Generated routes are attached automatically in Amala 13, so the returned app is ready to listen.

Type application context​

Koa accepts separate types for ctx.state and properties added directly to ctx. Amala preserves both:

import Koa from 'koa';
import {AmalaMiddleware, bootstrapControllers} from 'amala';

interface AppState {
  user?: User;
  services: Services;
}

interface ContextExtensions {
  requestId: string;
}

const app = new Koa<AppState, ContextExtensions>();

const requestContext: AmalaMiddleware<AppState, ContextExtensions> =
  async (ctx, next) => {
    ctx.state.services = services;
    ctx.requestId = crypto.randomUUID();
    await next();
  };

async function start() {
  await bootstrapControllers({
    app,
    controllers: [HealthController],
    flow: [requestContext],
  });

  app.listen(3000);
}

void start();

The typed application lets bootstrapControllers infer both generic arguments. When Amala creates the app, provide them explicitly with bootstrapControllers<AppState, ContextExtensions>(...).

These generics catch accidental undeclared context access at compile time. They do not validate middleware output or establish an authenticated identity.

Add validation​

Create src/controllers/UserController.ts:

import {
  Body,
  Controller,
  IsEmail,
  IsString,
  Post,
} from 'amala';

class CreateUserInput {
  @IsEmail()
  email!: string;

  @IsString()
  displayName!: string;
}

@Controller('/users')
export class UserController {
  @Post('/')
  create(@Body({required: true}) input: CreateUserInput) {
    return input;
  }
}

Register UserController beside HealthController. Amala transforms the JSON body into CreateUserInput, runs class-validator, and returns 422 when validation fails.

For strict object contracts, pass class-validator options during bootstrap as shown above.

Add middleware​

Use @Flow for controller- or endpoint-level Koa middleware:

import {
  AmalaMiddleware,
  Body,
  bootstrapControllers,
  Controller,
  Flow,
  Post,
} from 'amala';

const requireUser: AmalaMiddleware<AppState> = async (ctx, next) => {
  if (!ctx.state.user) {
    ctx.throw(401, 'Authentication required');
  }

  await next();
};

@Controller('/users')
class UserController {
  @Post('/')
  @Flow(requireUser)
  create(@Body({required: true}) input: CreateUserInput) {
    return input;
  }
}

async function start() {
  const {app} = await bootstrapControllers<AppState>({
    controllers: [UserController],
  });

  app.listen(3000);
}

void start();

Authentication and authorization are not built into Amala. Your middleware must establish identity and enforce access before the handler runs.

OpenAPI and Swagger​

OpenAPI is enabled by default. With basePath: '/api', Amala serves:

  • OpenAPI JSON at GET /api/docs
  • Swagger UI at GET /api/swagger

Set a public origin when the generated server URLs need an absolute URL:

const {app} = await bootstrapControllers({
  controllers: [HealthController, UserController],
  openAPI: {
    enabled: true,
    publicURL: 'https://api.example.com',
  },
});

app.listen(3000);

An omitted publicURL keeps Swagger on the same origin. Disable or protect these endpoints when your route inventory should not be public.

Attach routes manually​

Amala attaches generated routes by default. Set attachRoutes: false when you need to insert application middleware at a precise point before the router:

const {app, router} = await bootstrapControllers({
  attachRoutes: false,
  basePath: '/api',
  controllers: [HealthController, UserController],
});

app.use(yourMiddleware);
app.use(router.routes());
app.use(router.allowedMethods());

The option controls only where router middleware is mounted. Controller discovery and route generation still happen during bootstrap.

Continue with the bootstrapControllers reference and the production security guide.