This guide walks you through building a simple Users API with nestelia.

1. Create the Service

Services hold your business logic and are marked with @Injectable() so the DI container can manage them.

import { Injectable } from "nestelia";

@Injectable()
class UserService {
  private users = [{ id: 1, name: "John" }];

  findAll() {
    return this.users;
  }

  findById(id: number) {
    return this.users.find((u) => u.id === id);
  }

  create(user: { name: string }) {
    const newUser = { id: this.users.length + 1, ...user };
    this.users.push(newUser);
    return newUser;
  }
}

2. Create the Controller

Controllers define HTTP routes. Use @Controller to set a route prefix and HTTP decorators for individual methods.

import { t } from "elysia";
import { Controller, Get, Post, Body, Param, Inject, Ctx } from "nestelia";

@Controller("/users")
class UserController {
  constructor(@Inject(UserService) private readonly userService: UserService) {}

  @Get("/")
  getAll() {
    return this.userService.findAll();
  }

  @Get("/:id")
  getById(@Ctx() ctx: any) {
    return this.userService.findById(Number(ctx.params.id));
  }

  @Post("/")
  create(@Body(t.Object({ name: t.String() })) body: { name: string }) {
    return this.userService.create(body);
  }
}

INFO

@Body, @Param, and @Query accept a TypeBox schema for validation. To access individual route parameters without a schema, use @Ctx() to get the full Elysia context.

3. Create the Module

Modules group controllers and providers together. Every application has at least one root module.

import { Module } from "nestelia";

@Module({
  controllers: [UserController],
  providers: [UserService],
})
class AppModule {}

4. Bootstrap the Application

import { createElysiaApplication } from "nestelia";

const app = await createElysiaApplication(AppModule);
app.listen(3000, () => {
  console.log("Running on http://localhost:3000");
});

5. Test It

# List users
curl http://localhost:3000/users

# Get user by ID
curl http://localhost:3000/users/1

# Create a user
curl -X POST http://localhost:3000/users \
  -H "Content-Type: application/json" \
  -d '{"name": "Jane"}'

Full Example

import { t } from "elysia";
import {
  createElysiaApplication,
  Controller,
  Get,
  Post,
  Module,
  Body,
  Ctx,
  Inject,
  Injectable,
} from "nestelia";

@Injectable()
class UserService {
  private users = [{ id: 1, name: "John" }];

  findAll() {
    return this.users;
  }

  findById(id: number) {
    return this.users.find((u) => u.id === id);
  }

  create(user: { name: string }) {
    const newUser = { id: this.users.length + 1, ...user };
    this.users.push(newUser);
    return newUser;
  }
}

@Controller("/users")
class UserController {
  constructor(@Inject(UserService) private readonly userService: UserService) {}

  @Get("/")
  getAll() {
    return this.userService.findAll();
  }

  @Get("/:id")
  getById(@Ctx() ctx: any) {
    return this.userService.findById(Number(ctx.params.id));
  }

  @Post("/")
  create(@Body(t.Object({ name: t.String() })) body: { name: string }) {
    return this.userService.create(body);
  }
}

@Module({
  controllers: [UserController],
  providers: [UserService],
})
class AppModule {}

const app = await createElysiaApplication(AppModule);
app.listen(3000);

Next Steps

• Modules — Learn how to organize your app with modules.
• Dependency Injection — Understand DI scopes and custom providers.