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di-wise 🧙‍♀️

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Lightweight and flexible dependency injection library for JavaScript and TypeScript, w/wo ECMAScript decorators.

Table of Contents

Installation

npm install di-wise

pnpm add di-wise

yarn add di-wise

Also available on JSR:

deno add jsr:@exuanbo/di-wise

Features

Zero dependencies

Modern decorator implementation

Context-based DI system

  • Flexible decorator-based or function-based injection
  • Full type inference support ✨
  • Optional decorators with equivalent function alternatives

Example:

import {createContainer, Inject, inject, Injectable, Scope, Scoped, Type} from "di-wise";

interface Spell {
  cast(): void;
}
const Spell = Type<Spell>("Spell");

@Scoped(Scope.Container)
@Injectable(Spell)
class Fireball implements Spell {
  cast() {
    console.log("🔥");
  }
}

class Wizard {
  @Inject(Wand)
  wand!: Wand;

  // Equivalent to
  wand = inject(Wand);

  constructor(spell = inject(Spell)) {
    // inject() can be used anywhere during construction
    this.wand.store(spell);
  }
}

const container = createContainer();
container.register(Fireball);

// Under the hood
[Fireball, Spell].forEach((token) => {
  container.register(
    token,
    {useClass: Fireball},
    {scope: Scope.Container},
  );
});

const wizard = container.resolve(Wizard);
wizard.wand.activate(); // => 🔥

Multiple provider types

  • Class, Factory, and Value providers
  • Built-in helpers for one-off providers: Build(), Value()
  • Seamless integration with existing classes

Example:

import {Build, createContainer, inject, Value} from "di-wise";

class Wizard {
  equipment = inject(
    Cloak,
    // Provide a default value
    Value({
      activate() {
        console.log("👻");
      },
    }),
  );

  wand: Wand;

  constructor(wand: Wand) {
    this.wand = wand;
  }
}

const container = createContainer();

const wizard = container.resolve(
  Build(() => {
    // inject() can be used in factory functions
    const wand = inject(Wand);
    return new Wizard(wand);
  }),
);

wizard.equipment.activate(); // => 👻

Hierarchical injection

  • Parent-child container relationships
  • Automatic token resolution through the container hierarchy
  • Isolated registration with shared dependencies

Example:

import {createContainer, inject, Injectable, Type} from "di-wise";

const MagicSchool = Type<string>("MagicSchool");
const Spell = Type<{cast(): void}>("Spell");

// Parent container with shared config
const hogwarts = createContainer();
hogwarts.register(MagicSchool, {useValue: "Hogwarts"});

@Injectable(Spell)
class Fireball {
  school = inject(MagicSchool);
  cast() {
    console.log(`🔥 from ${this.school}`);
  }
}

// Child containers with isolated spells
const gryffindor = hogwarts.createChild();
gryffindor.register(Fireball);

const slytherin = hogwarts.createChild();
slytherin.register(Spell, {
  useValue: {cast: () => console.log("🐍")},
});

gryffindor.resolve(Spell).cast(); // => 🔥 from Hogwarts
slytherin.resolve(Spell).cast();  // => 🐍

Full control over registration and caching

  • Explicit container management without global state
  • Fine-grained control over instance lifecycle
  • Transparent registry access for testing

Various injection scopes

  • Flexible scoping system: Inherited (default), Transient, Resolution, Container
  • Smart scope resolution for dependencies
  • Configurable default scopes per container

Example for singleton pattern:

import {createContainer, Scope} from "di-wise";

export const singletons = createContainer({
  defaultScope: Scope.Container,
  autoRegister: true,
});

// Always resolves to the same instance
const wizard = singletons.resolve(Wizard);

Inherited (default)

Inherits the scope from its dependent. If there is no dependent (top-level resolution), behaves like Transient.

Example 
import {createContainer, Scope, Scoped} from "di-wise";

@Scoped(Scope.Container)
class Wizard {
  wand = inject(Wand);
}

const container = createContainer();
container.register(
  Wand,
  {useClass: Wand},
  {scope: Scope.Inherited},
);
container.register(Wizard);

// Dependency Wand will be resolved with "Container" scope
const wizard = container.resolve(Wizard);

Transient

Creates a new instance every time the dependency is requested. No caching occurs.

Resolution

Creates one instance per resolution graph. The same instance will be reused within a single dependency resolution, but new instances are created for separate resolutions.

Example 
@Scoped(Scope.Resolution)
class Wand {}

class Inventory {
  wand = inject(Wand);
}

class Wizard {
  inventory = inject(Inventory);
  wand = inject(Wand);
}

const container = createContainer();
const wizard = container.resolve(Wizard);

expect(wizard.inventory.wand).toBe(wizard.wand);

Container

Creates one instance per container (singleton pattern). The instance is cached and reused for all subsequent resolutions within the same container.

Flexible token-based injection

  • Multiple token resolution with union type inference ✨
  • Support for optional dependencies via Type.Null and Type.Undefined
  • Interface-based token system

Example:

import {inject, Type} from "di-wise";

class Wizard {
  wand = inject(Wand, Type.Null);
  // ^? (property) Wizard.wand: Wand | null
}

Automatic circular dependency resolution

  • Smart handling of circular dependencies
  • Multiple resolution strategies (@Inject() or inject.by())
  • Maintains type safety

Example:

import {createContainer, Inject, inject} from "di-wise";

class Wand {
  owner = inject(Wizard);
}

class Wizard {
  @Inject(Wand)
  wand!: Wand;

  // Equivalent to
  wand = inject.by(this, Wand);
}

const container = createContainer();
const wizard = container.resolve(Wizard);

expect(wizard.wand.owner).toBe(wizard);

Dynamic injection

  • On-demand dependency resolution via Injector
  • Context-aware lazy loading
  • Preserves proper scoping and circular dependency handling

Example:

import {createContainer, inject, Injector} from "di-wise";

class Wizard {
  private injector = inject(Injector);
  private wand?: Wand;

  getWand() {
    // Lazy load wand only when needed
    return (this.wand ??= this.injector.inject(Wand));
  }

  castAllSpells() {
    // Get all registered spells
    const spells = this.injector.injectAll(Spell);
    spells.forEach((spell) => spell.cast());
  }
}

const container = createContainer();
const wizard = container.resolve(Wizard);

wizard.getWand(); // => Wand

The injector maintains the same resolution context as its injection point, allowing proper handling of scopes and circular dependencies:

import {createContainer, inject, Injector} from "di-wise";

class Wand {
  owner = inject(Wizard);
}

class Wizard {
  private injector = inject.by(this, Injector);

  getWand() {
    return this.injector.inject(Wand);
  }
}

const container = createContainer();
const wizard = container.resolve(Wizard);

const wand = wizard.getWand();
expect(wand.owner).toBe(wizard);

Constructor Injection

See discussion Does di-wise support constructor injection? #12

Middleware

  • Extensible container behavior through middleware
  • Composable middleware chain with predictable execution order
  • Full access to container lifecycle

Example:

import {applyMiddleware, createContainer, type Middleware} from "di-wise";

const logger: Middleware = (composer, _api) => {
  composer
    .use("resolve", (next) => (token) => {
      console.log("Resolving:", token.name);
      const result = next(token);
      console.log("Resolved:", token.name);
      return result;
    })
    .use("resolveAll", (next) => (token) => {
      console.log("Resolving all:", token.name);
      const result = next(token);
      console.log("Resolved all:", token.name);
      return result;
    });
};

const performanceTracker: Middleware = (composer, _api) => {
  composer.use("resolve", (next) => (token) => {
    const start = performance.now();
    const result = next(token);
    const end = performance.now();
    console.log(`Resolution time for ${token.name}: ${end - start}ms`);
    return result;
  });
};

const container = applyMiddleware(createContainer(), [logger, performanceTracker]);

// Use the container with applied middlewares
const wizard = container.resolve(Wizard);

Middlewares are applied in array order but execute in reverse order, allowing outer middlewares to wrap and control the behavior of inner middlewares.

Usage

🏗️ WIP (PR welcome)

API

See API documentation.

Credits

Inspired by:

License

MIT License @ 2024-Present Xuanbo Cheng