iti

🚧 library is in beta mode 🚧

Iti

~1kB inversion of control container for Typescript/Javascript for constructor injection with a focus on async flow

• fully async: merges async code and a constructor injection via async functions (asynchronous factory pattern)
• non-invasive: does not require library @decorators or framework extends in your application logic
• lazy: initialises your app modules and containers on demand
• split chunks: enables dynamic imports via a one liner thanks to a fully async core
• Strongly typed: With great IDE autocomplete and compile tme check. Works without manual type casting
• lightweight: doesn't rely on reflect-metadata or decorators
• starter friendly: works with starters like Create React App or Next.js unlike InversifyJS or microsoft/tsyringe
• no Babel config: it doesn't require reflect-metadata or decorators so there are no need to hack in decorator and "decoratorMetadata" support into Create React App, node.js, next.js, snowpack, esbuild etc.
• React support: has useful React bindings to help separate application logic and React view layer
• tiny: less than 2kB

iti is an alternative to InversifyJS and microsoft/tsyringe. It relies on plain JS functions, objects and familiar patterns. There is no need to learn complex API to use it in a full capacity.

Usage

npm install -S iti

Basic Usage

// Step 1: Your application logic stays clean
class Oven {
  public pizzasInOven() {
    return 3
  }
  public async preheat() {}
}
class Kitchen {
  constructor(public oven: Oven, public manual: string) {}
}

// Step 2: Add and read simple tokens
import { makeRoot } from "iti"
let root = makeRoot().add({
  userManual: "Please preheat before use",
  oven: () => new Oven(),
})
root.get("oven")

// Step 3: Add a usefull async provider / container
const kitchenContainer = async ({ oven, userManual }) => {
  await oven.preheat()
  return {
    kitchen: new Kitchen(oven, userManual),
  }
}
// Step 4: Add an async provider
const node = root.add((containers, node) => ({
  kitchen: async () =>
    kitchenContainer(await node.getContainerSet(["userManual", "oven"])),
}))
root.get("oven") // Oven
await node.get("kitchen") // { kitchen: Kitchen }

// Typical React usage
export const PizzaData = () => {
  const [oven] = useContainer().oven
  return <> Pizzaz In Oven: {oven.pizzasInOven()}</>
}

Why another library?

Libraries like InversifyJS or tsyringe rely on decorators and reflect-metadata.

Firstly, decorators unnecessary couple your application logic with a framework.

Secondly, it is very hard to use with starters like CRA, Next.js etc. To use reflect-metadata you need to configure your compiler (babel, typescrip, esbuild, swc etc.) configuratoin which is not trivial. So if you can’t use reflect-metadata you can't use inversify.

Short Manual

Reading

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

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

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

// Subscribe to container changes
node.subscribeToContiner("oven", (oven) => {})
node.subscribeToContinerSet(["oven", "kitchen"], ({ oven, kitchen }) => {})
// prettier-ignore
node.subscribeToContinerSet((c) => [c.kitchen], ({ oven, kitchen }) => {})
node.on("containerUpdated", ({ key, newContainer }) => {})
node.on("containerUpserted", ({ key, newContainer }) => {})

Writing

let node1 = makeRoot()
  .add({
    userManual: "Please preheat before use",
    oven: () => new Oven(),
  })
  .upsert((containers, node) => ({
    userManual: "Works better when hot",
    preheatedOven: async () => {
      await containers.oven.preheat()
      return containers.oven
    },
  }))

// `add` is typesafe and a runtime safe method. Hence we've used `upsert`
try {
  node1.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

Single Instance (a.k.a. Singleton)

import { Oven, Kitchen } from "./kitchen/"
export async function provideKitchenContainer() {
  const oven = new Oven()
  await oven.preheat()

  return {
    kitchen: new Kitchen(),
    oven: oven,
  }
}

Transient

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

Dynamic Imports

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
    },
  }
}

Tip: Prefer callbacks over of strings (in progress)

If you use callback pattern across your app, you will be able to mass rename your containerKeys using typescript. With strings, you will have to manually go through the app. On the bright side, compiler will not compile until you fix your rename manually across the app.

const node = makeRoot().addNode({
  a: "A",
  b: "B",
})

await node.get((containerKeys) => containerKeys.a) // BEST!!!
await node.get("a") // it will work but...

Tip: Prefer sealing your node

This will help resolve some very exotic race conditions with subscriptions and container updates. We internally seal() our node on every get request but you can do it too before non trivial operations

await makeRoot()
  .addPromise(async () => ({
    a: "A",
    b: "B",
  }))
  .seal() // Good

Anti Patterns

Getting Started

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

Initial wiring

import { makeRoot } from "../../src/library.new-root-container"

import { provideAContainer } from "./container.a"
import { provideBContainer } from "./container.b"
import { provideCContainer } from "./container.c"

export type MockAppNode = ReturnType<typeof getMainMockAppContainer>
export function getMainMockAppContainer() {
  let node = makeRoot()
  let k = node
    .add({ aCont: async () => provideAContainer() })
    .add((containers) => {
      return {
        bCont: async () => provideBContainer(await containers.aCont),
      }
    })
    .add((c) => {
      return {
        cCont: async () => provideCContainer(await c.aCont, await c.bCont, k),
      }
    })
  return k
}

Typescript

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

Docs

Tokens

Containers

Containers are an important unit. If you replace them, users will be notified. In React it happens automatically

Events

const kitchenApp = new RootContainer((ctx) => ({
  // you can use tokens (`oven`, `kitchen`) here and later on
  oven: async () => ovenContainer(),
  kitchen: async () => kitchenContainer(await ctx.oven()),
}))

kitchenApp.on("containerCreated", (event) => {
  console.log(`event: 'containerCreated' ~~> token: '${event.key}'`)
  // `event.container` is also avaliable here
})

kitchenApp.on("containerRequested", (event) => {
  console.log(`event: 'containerRequested' ~~> token: '${event.key}' `)
})

kitchenApp.on("containerRemoved", (event) => {
  console.log(`event: 'containerRemoved' ~~> token: '${event.key}' `)
})

await kitchenApp.containers.kitchen

// event: 'containerRequested' ~~> token: 'kitchen'
// event: 'containerRequested' ~~> token: 'oven'
// event: 'containerCreated'   ~~> token: 'oven'
// event: 'containerCreated'   ~~> token: 'kitchen'

// Notice how oven was created before kitchen.
// This is because kitcen depends on oven

API documentation JS / TS

makeRoot Setting app root

import { makeRoot, RootContainer } from "../../library.root-container"
export function getMainMockAppContainer() {
  // check get providers above
  return makeRoot(getProviders)
}

containers getter

let appRoot = getMainPizzaAppContainer()
let kitchen = await appRoot.containers.kitchen
kitchen.oven.pizzaCapacity // 4

getContainerSet

getContainerSetNew

upsert

When containers are updated React is updated too via hooks

Comparison with inversifyjs, tsyringe and others

Inversion of Control (IoC) is a great way to decouple the application and the most popular pattern of IoC is dependency injection (DI) but it is not limited to one.

In JavaScript there is not way to create a dependency injection without mixing application logic with a specific IoC library code or hacking a compiler (reflect-metadata).

inversifyjs and tsyringe use decorators and reflect-metada

import { injectable } from "tsyringe"

@injectable()
class Foo {
  constructor(private database: Database) {}
}

// some other file
import "reflect-metadata"
import { container } from "tsyringe"
import { Foo } from "./foo"

const instance = container.resolve(Foo)

typed-inject uses monkey-patching

import { createInjector } from "typed-inject"
function barFactory(foo: number) {
  return foo + 1
}
barFactory.inject = ["foo"] as const
class Baz {
  constructor(bar: number) {
    console.log(`bar is: ${bar}`)
  }
  static inject = ["bar"] as const
}

With Iti your application logic is not mixed with the framework code

import type { Ingredients } from "./store.ingrediets"
import type { Oven } from "./store.oven"

export class Kitchen {
  constructor(private oven: Oven, private ingredients: Ingredients) {}
}

// provider / factory
import { IngredientsService } from "../services/ingredients-manager"
import { Kitchen } from "../stores/store.kitchen"
import { Oven } from "../stores/store.oven"

export async function provideKitchenContainer() {
  let oven = new Oven()
  let ingredients = await IngredientsService.buySomeIngredients()
  let kitchen = new Kitchen(oven, ingredients)

  return {
    oven: oven,
    ingredients: ingredients,
    kitchen: kitchen,
  }
}

Notable inspirations:

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

Questions and tips

Can I have multiple application containers?

Yes, no problem at all. If you want, they can even share tokens and hence instances!

Why getContainerSet is always async?

This is temporary(?) limitation to keep typescript happy and typescript types reasonable sane