Iti
1kB inversion of control container for Typescript and Javascript with a unique feature that supports async flow
- 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: initialises 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
export class Oven {
public pizzasInOven() {
return 7
}
public async preheat() {}
}
export class Kitchen {
constructor(public oven: Oven, public userManual: string) {}
}
import { makeRoot } from "iti"
import { Oven, Kitchen } from "./kitchen"
const node = makeRoot()
.add({
oven: () => new Oven(),
userManual: async () => "Please preheat before use",
})
.add((ctx) => ({
kitchen: async () => new Kitchen(ctx.oven, await ctx.userManual),
}))
await node.get("kitchen")
export const PizzaData = () => {
const kitchen = useContainer().kitchen
return <>Pizzaz 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
root.get("oven")
root.get("oven")
await node.get("kitchen")
await node.containers.kitchen
await root.getContainerSet(["oven", "userManual"])
await root.getContainerSet((c) => [c.userManual, c.oven])
node.subscribeToContiner("oven", (oven) => {})
node.subscribeToContinerSet(["oven", "kitchen"], ({ oven, kitchen }) => {})
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
},
}))
try {
node1.add({
userManual: "You shall not pass",
})
} catch (err) {
err.message
}
Patterns and tips
Lifecycle
Single Instance (a.k.a. Singleton)
let node = makeRoot().add({
oven: () => new Oven(),
})
node.get("oven") === node.get("oven")
Transient
let node = makeRoot().add({
oven: () => () => new Oven(),
})
node.get("oven") === node.get("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
},
}
}
import { makeRoot } from "iti"
import { provideKitchenContainer } from "./kitchen"
let node = makeRoot().add({
kitchen: async () => provideKitchenContainer(),
})
await node.containers.kitchen
await node.containers.kitchen.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. But even if you use string literals 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)
await node.get("a")
Anti Patterns
in progress
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() {
return makeRoot()
.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),
}
})
}
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) => ({
oven: async () => ovenContainer(),
kitchen: async () => kitchenContainer(await ctx.oven()),
}))
kitchenApp.on("containerCreated", (event) => {
console.log(`event: 'containerCreated' ~~> token: '${event.key}'`)
})
kitchenApp.on("containerRequested", (event) => {
console.log(`event: 'containerRequested' ~~> token: '${event.key}' `)
})
kitchenApp.on("containerRemoved", (event) => {
console.log(`event: 'containerRemoved' ~~> token: '${event.key}' `)
})
await kitchenApp.containers.kitchen
API documentation JS / TS
makeRoot
Setting app root
import { makeRoot } from "../../library.root-container"
export function getMainMockAppContainer() {
return makeRoot().add({ kitchen: () => new Kitchen() })
}
containers
getter
let appRoot = getMainPizzaAppContainer()
let kitchen = await appRoot.containers.kitchen
kitchen.oven.pizzaCapacity
getContainerSet
getContainerSetNew
upsert
When containers are updated React is updated too via hooks
Alternaitves
No async support
Existing libraries like inversify and others don’t support asynchronous code.
They either provide a promise to your constructor or require one to imperatively execute all potentially async code before the binding phase.
This is far from ideal.
Heavy use of decorators
Secondly, they rely on decorators and reflect-metadata
Decorators create unnecessary coupling of an application business logic with a framework. The whole idea of DI is to decouple the application business logic. Coupling classes with a DI framework is still coupling and turns DI into a service locator.
Also, decorator support is an experimental feature in Typescript and current implementation is not compatible with the TC39 proposal. This will probably cause problems for any non-trivial decorators and babel hacks.
In addition to that it is very hard to use reflect-metadata
with starters like CRA, Next.js etc. To use reflect-metadata
you need to tweak your compilers (babel, typescript, esbuild, swc etc.) configuration. So if you can’t use reflect-metadata
you can’t use inversify
or tsyringe
.
Comparison with inversifyjs
, tsyringe
and others
Inversion of Control (IoC) is a great way to decouple code 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 business 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) {}
}
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 business 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) {}
}
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:
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