App Leaf Package

A lightweight, decorator-based lifecycle and dependency injection framework for TypeScript applications.

Installation

# Using npm
npm install app-leaf

# Using Bun
bun add app-leaf

Important Import Warning

When using controllers, always use regular imports rather than type-only imports:

import type { SomeController } from "./SomeController"; // BAD: Will cause errors during dependency injection

import { SomeController } from "./SomeController"; // GOOD: Ensures proper controller registration

Type-only imports prevent the controller class from being registered properly in the dependency injection system.

Features

• Decorator-based controller registration
• Controlled lifecycle with initialization and start hooks
• Automatic dependency injection
• Module system for organizing controllers
• Prevention of cyclic dependencies
• Load order control

Usage

Basic Example

import { Controller, OnInit, OnStart, AppLeaf } from "app-leaf";

@Controller()
class HelloController {
  @OnInit()
  private init() {
    console.log("HelloController initialized");
  }

  @OnStart()
  private start() {
    console.log("HelloController started");
  }

  sayHello() {
    return "Hello, world!";
  }
}

@Controller()
class AppController {
  constructor(private readonly helloController: HelloController) {}

  @OnStart()
  private start() {
    console.log(this.helloController.sayHello());
  }
}

// Start the application lifecycle
AppLeaf.Start();

Using Modules

import { Controller, Module, AppLeaf } from "app-leaf";

@Controller()
class UserController {
  getUsers() {
    return ["User1", "User2"];
  }
}

@Controller()
class ProductController {
  getProducts() {
    return ["Product1", "Product2"];
  }
}

@Module([UserController, ProductController])
class FeatureModule {}

// To ensure all controllers are imported
AppLeaf.LoadModules([FeatureModule]);
AppLeaf.Start();

Controlling Load Order

@Controller({ loadOrder: 1 })
class FirstController {}

@Controller({ loadOrder: 2 })
class SecondController {}

Using the Dependency Utility

import { Controller, OnStart, Dependency, AppLeaf } from "app-leaf";

@Controller()
class ServiceController {
  getData() {
    return "Service Data";
  }
}

@Controller()
class ConsumerController {
  @OnStart()
  private start() {
    // Get controller reference after initialization
    const service = Dependency(ServiceController);
    console.log(service.getData());
  }
}

AppLeaf.Start();

API Reference

Decorators

@Controller(options?: { loadOrder?: number })

Registers a class as a controller in the application lifecycle.

• loadOrder: Optional number that determines initialization order (lower values initialize first)

@OnInit()

Marks a method to be called during the initialization phase, before dependency injection.

@OnStart()

Marks a method to be called after all controllers are initialized and injected.

@Module(controllers: any[])

Registers a class as a module containing a list of controllers.

Functions

Dependency<T>(controllerClass: new (...args: any) => T): T

Gets an instance of a registered controller after initialization.

• Should primarily be used within OnStart methods or after AppLeaf.Start()
• Throws error if controller is not registered or not loaded yet

AppLeaf Namespace

AppLeaf.LoadModules(modules: any[])

Ensures that all controllers in the provided modules are imported.

AppLeaf.Start()

Starts the application lifecycle:

1. Initializes all controllers in order of their loadOrder
2. Resolves dependencies between controllers
3. Calls OnInit methods
4. Calls all OnStart methods in parallel

Important Notes

• If a controller fails in constructor - app stops
• If a controller fails in OnInit - app stops
• If a controller fails in OnStart - it logs a warning but the app continues running
• Cyclic dependencies are detected and prevented