@fxfn/inject

A zero-dependency DI container using TypeScript 5 standard decorators. No experimentalDecorators, no emitDecoratorMetadata, no reflect-metadata.

Install

bun add @fxfn/inject

Register and resolve

import { container } from "@fxfn/inject";

// Interface → implementation
container.register(IUserService, UserService);
const svc = container.resolve(IUserService); // new instance each time

// Singleton
container.register(IRouter, RouterService, { singleton: true });
const router = container.resolve(IRouter); // same instance every time

// Symbol token with a plain value
const ApiKey = Symbol("ApiKey");
container.register(ApiKey, process.env.API_KEY!);

Decorators

@inject and @injectall use the TC39 standard accessor keyword for lazy resolution.

import { inject, injectall } from "@fxfn/inject";

class MyService {
  @inject(IConfig)
  accessor config!: IConfig;

  @injectall(IRoute)
  accessor routes!: IRoute[];
}

Dependencies are resolved on first property access, not at construction time.

Tagged injection

Distinguish between multiple registrations of the same token:

container.register(IDatabase, PrimaryDb, { singleton: true, tag: "primary" });
container.register(IDatabase, ReplicaDb, { singleton: true, tag: "replica" });

class MyService {
  @inject(IDatabase, { tag: "primary" })
  accessor db!: IDatabase;
}

When resolving without a tag, the first untagged registration wins. If none is untagged, the first registration is used as a fallback.

Package exports

Import	What it provides
@fxfn/inject	container, Container, inject, injectall, IContainer, Token, Constructor, RegistrationOptions, ResolveContext

Documentation

Topic	Description
Container	register, resolve, resolveAll, singleton and transient lifetimes
Decorators	@inject, @injectall, tagged injection, lazy resolution