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~1kB inversion of control container for Typescript/Javascrith with a focus on async flow
1kB inversion of control container for Typescript and Javascript with a unique feature that supports async flow
@decorators
or framework extends
in your application business logicreflect-metadata
or decorators so there is no need to hack in decorator and "decoratorMetadata"
support in to your build configsIoC 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
// 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 { 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") // Kitchen
// MyPizzaComponent.tsx
export const PizzaData = () => {
const kitchen = useContainer().kitchen
return <>Pizzaz In Oven: {kitchen.oven.pizzasInOven()}</>
}
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.
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']
}
Single Instance (a.k.a. Singleton)
let node = makeRoot().add({
oven: () => new Oven(),
})
node.get("oven") === node.get("oven") // true
Transient
let node = makeRoot().add({
oven: () => () => new Oven(),
})
node.get("oven") === node.get("oven") // false
// ./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 { makeRoot } from "iti"
import { provideKitchenContainer } from "./kitchen"
let node = makeRoot().add({
kitchen: async () => provideKitchenContainer(),
})
// Next line will load `./kitchen/kitchen` module
await node.containers.kitchen
// Next line will load `./kitchen/oven` module
await node.containers.kitchen.oven
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) // BEST!!!
await node.get("a") // it will work but...
in progress
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),
}
})
}
Iti has a great typescript support. All types are resolved automatically and check at compile time.
Containers are an important unit. If you replace them, users will be notified. In React it happens automatically
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
makeRoot
Setting app rootimport { makeRoot } from "../../library.root-container"
export function getMainMockAppContainer() {
return makeRoot().add({ kitchen: () => new Kitchen(/* deps */) })
}
containers
getterlet 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
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.
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
.
inversifyjs
, tsyringe
and othersInversion 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) {}
}
// 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 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) {}
}
// 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:
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
Kudos to typed-inject for finding a reasonable alternative to decorators and Reflect. Sadly, it doesn't support async and there are some other limits ↩
FAQs
~1kB Dependency Injection Library for Typescript and React with a unique async flow support
We found that iti demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 0 open source maintainers collaborating on the project.
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