Iti

~1kB Dependency Injection Library for Typescript and React with a unique async flow support

• supports async(!): merges async code and constructor injection via plain async functions
• non-invasive: does not require imported @decorators or framework extends in your application business logic
• strongly typed: has great IDE autocomplete and compile time check. Without any manual type casting
• lazy: initializes your app modules and containers on demand
• split chunks: enables dynamic imports via a one liner thanks to a fully async core
• React friendly: has useful React bindings to help you separate application business logic and a React view layer
• starter friendly: works with starters like Create React App or Next.js unlike existing libraries
• no Babel config: doesn't require reflect-metadata or decorators so there is no need to hack in decorator and "decoratorMetadata" support in to your build configs
• tiny: less than 1kB

IoC is an amazing pattern and it should easy to adopt, fully support async and without hard to learn APIs or complex tooling requirements.

Iti relies on plain JS functions, objects and familiar patterns. API is simple so you can make a proof of concept integration in minutes.

It is an alternative to InversifyJS and microsoft/tsyringe for constructor injection.

At Packhelp we’ve refactored most of our 65K SLOC Editor app, that didn't have any IoC, to Iti in under 5 hours

Usage

// kitchen.ts
export class Oven {
  public pizzasInOven() {
    return 7
  }
  public async preheat() {}
}
export class Kitchen {
  constructor(public oven: Oven, public userManual: string) {}
}
// Application code is free of framework dependencies of decorators

// app.ts
import { createContainer } from "iti"
import { Oven, Kitchen } from "./kitchen"

const container = createContainer()
  .add({
    key: () => new Item(),
    oven: () => new Oven(),
    userManual: async () => "Please preheat before use",
  })
  .add((items) => ({
    kitchen: async () => new Kitchen(items.oven, await items.userManual),
  }))

await container.get("kitchen") // Kitchen

// MyPizzaComponent.tsx
export const PizzaData = () => {
  const kitchen = useContainer().kitchen
  return <>Pizzas In Oven: {kitchen.oven.pizzasInOven()}</>
}

Why another library?

The main reason is that existing libraries don’t support asynchronous code. Iti brings hassle free and fully typed way to use async code.

Secondly, existing libraries rely on decorators and reflect-metadata[^1]. They couple your application business logic with a single framework and they tend to become unnecessarily complex. Also existing implementations will likely be incompatible with a TC39 proposal.

Also it is hard to use reflect-metadata with starters like CRA, Next.js etc. You need to eject or hack starters and it is far from ideal.

Short Manual

Reading

// Get a single instance
container.get("oven") // Creates a new Oven instance
container.get("oven") // Gets a cached Oven instance

await container.get("kitchen") // { kitchen: Kitchen } also cached
await container.items.kitchen // same as above

// Get multiple instances at once
await container.getContainerSet(["oven", "userManual"]) // { userManual: '...', oven: Oven }
await container.getContainerSet((c) => [c.userManual, c.oven]) // same as above

// Plain deletion
container.delete("kitchen")

// Subscribe to container changes
container.subscribeToContainer("oven", (oven) => {})
container.subscribeToContainerSet(
  ["oven", "kitchen"],
  ({ oven, kitchen }) => {},
)
// prettier-ignore
container.subscribeToContainerSet((c) => [c.kitchen], ({ oven, kitchen }) => {})
container.on("containerUpdated", ({ key, newItem }) => {})
container.on("containerUpserted", ({ key, newItem }) => {})
container.on("containerDeleted", ({ key, newItem }) => {})

// Disposing
container
  .add({ dbConnection: () => connectToDb(process.env.dbUrl) })
  .addDisposer({ dbConnection: (db) => db.disconnect() }) // waits for promise
await container.dispose("dbConnection")
await container.disposeAll()

Writing

let container = createContainer()
  .add({
    userManual: "Please preheat before use",
    oven: () => new Oven(),
  })
  .upsert((items, cont) => ({
    userManual: "Works better when hot",
    preheatedOven: async () => {
      await items.oven.preheat()
      return items.oven
    },
  }))

// `add` is typesafe and a runtime safe method. Hence we've used `upsert`
try {
  container.add({
    // @ts-expect-error
    userManual: "You shall not pass",
    // Type Error: (property) userManual: "You are overwriting this token. It is not safe. Use an unsafe `upsert` method"
  })
} catch (err) {
  err.message // Error Tokens already exist: ['userManual']
}

Patterns and tips

Lifecycle

Single Instance (a.k.a. Singleton)

let cont = createContainer().add({
  oven: () => new Oven(),
})
cont.get("oven") === cont.get("oven") // true

Transient

let cont = createContainer().add({
  oven: () => () => new Oven(),
})
cont.get("oven") === cont.get("oven") // false

Dynamic Imports

// ./kitchen/index.ts
export async function provideKitchenContainer() {
  const { Kitchen } = await import("./kitchen/kitchen")
  return {
    kitchen: () => new Kitchen(),
    oven: async () => {
      const { Oven } = await import("./kitchen/oven")
      const oven = new Oven()
      await oven.preheat()
      return oven
    },
  }
}

// ./index.ts
import { createContainer } from "iti"
import { provideKitchenContainer } from "./kitchen"
let cont = createContainer().add({
  kitchen: async () => provideKitchenContainer(),
})

// Next line will load `./kitchen/kitchen` module
await cont.items.kitchen

// Next line will load `./kitchen/oven` module
await cont.items.kitchen.oven

Getting Started

The best way to get started is to check a CRA Pizza example

Typescript

Iti has a great typescript support. All types are resolved automatically and checked at compile time.

Docs

Read more at itijs.org/docs/api

Notable inspiration

• https://github.com/nicojs/typed-inject
• https://github.com/microsoft/tsyringe
• https://github.com/asvetliakov/Huject https://github.com/jeffijoe/awilix
• https://github.com/typestack/typedi
• https://github.com/inversify/InversifyJS