@wessberg/di

DI (Dependency Injector)

A Dependency-Injection container that holds services and can produce instances of them as required. It mimics reflection by parsing the app at compile-time and supporting the generic-reflection syntax.

Installation

Simply do: npm install @wessberg/di.

Description

DI is truly a fresh take on dependency injection in a TypeScript/JavaScript environment:

• It does its work on compile-time. The only runtime dependency is the DIContainer itself, which is tiny.
• It doesn't ask you to reflect metadata or to annotate your classes with decorators. "It just works".
• It maps interfaces to implementations. Most popular dependency injection systems for TypeScript doesn't do this. This allows you to truly decouple an abstraction from its implementation.
• It supports the .NET generic reflection flavour: registerSingleton<Interface, Implementation>(). No need for anything else.

Usage

import {DIContainer} from "@wessberg/di";
DIContainer.registerSingleton<IFoo, Foo>();
DIContainer.registerTransient<IBar, Bar>();
DIContainer.get<IBar>(); // Retrieves a concrete instance of the IBar service.

// And so on...

Overwriting a new-expression for a custom constructor

Sometimes, you may want to invoke the constructor of a service with custom arguments, rather than relying on every other non-initialized parameter of the service constructor to be dependency injected. You can do that by passing a function that returns a new instance of the provided service as the first argument registerSingleton or registerTransient.

DIContainer.registerSingleton<IFoo, Foo>(() => new Foo("customArg", 123, "foo"));

Making it work

To make the injections work - and to support the generic reflection notation - you need to compile the source code with the DI-Compiler.

If you are using Rollup, then use rollup-plugin-di to compile your code automatically as part of your bundle.

How does it work

It uses CodeAnalyzer to check all of your code and all of its dependencies recursively to track classes and the constructor arguments they take (and their order). When a DIContainer constructs a new instance of a service, it knows which concrete implementations match interfaces that exists in the signature of class constructors.