TSyringe

A lightweight dependency injection container for TypeScript/JavaScript for constructor injection.

<!-- TOC depthFrom:1 depthTo:3 -->

• TSyringe
  • Installation
• API
  • Decorators
    • injectable()
    • singleton()
    • autoInjectable()
    • inject()
    • injectAll()
    • injectWithTransform()
    • injectAllWithTransform()
    • scoped()
  • Container
    • Injection Token
    • Providers
    • Register
    • Registry
    • Resolution
    • IsRegistered
    • Interception
    • Child Containers
    • Clearing Instances
• Circular dependencies
  • The delay helper function
  • Interfaces and circular dependencies
• Disposable instances
• Full examples
  • Example without interfaces
  • Example with interfaces
  • Injecting primitive values (Named injection)
• Non goals
• Contributing

<!-- /TOC -->

Installation

Install by npm

npm install --save tsyringe

or install with yarn (this project is developed using yarn)

yarn add tsyringe

Modify your tsconfig.json to include the following settings

{
  "compilerOptions": {
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true
  }
}

Add a polyfill for the Reflect API (examples below use reflect-metadata). You can use:

• reflect-metadata
• core-js (core-js/es7/reflect)
• reflection

The Reflect polyfill import should only be added once, and before DI is used:

// main.ts
import "reflect-metadata";

// Your code here...

Babel

If you're using Babel (e.g. using React Native), you will need to configure it to emit TypeScript metadata.

First get the Babel plugin

Yarn

yarn add --dev babel-plugin-transform-typescript-metadata

npm

npm install --save-dev babel-plugin-transform-typescript-metadata

Then add it to your Babel config

plugins: [
            'babel-plugin-transform-typescript-metadata',
            /* ...the rest of your config... */
         ]

API

TSyringe performs Constructor Injection on the constructors of decorated classes.

Decorators

injectable()

Class decorator factory that allows the class' dependencies to be injected at runtime. TSyringe relies on several decorators in order to collect metadata about classes to be instantiated.

Usage

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);

singleton()

Class decorator factory that registers the class as a singleton within the global container.

Usage

import {singleton} from "tsyringe";

@singleton()
class Foo {
  constructor() {}
}

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

const instance = container.resolve(Foo);

autoInjectable()

Class decorator factory that replaces the decorated class' constructor with a parameterless constructor that has dependencies auto-resolved.

Note Resolution is performed using the global container.

Usage

import {autoInjectable} from "tsyringe";

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

// some other file
import {Foo} from "./foo";

const instance = new Foo();

Notice how in order to allow the use of the empty constructor new Foo(), we need to make the parameters optional, e.g. database?: Database.

inject()

Parameter decorator factory that allows for interface and other non-class information to be stored in the constructor's metadata.

Usage

import {injectable, inject} from "tsyringe";

interface Database {
  // ...
}

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

Optional

By default, @inject() throws an exception if no registration is found. If you want to have undefined injected when the registration isn't found, you can pass this options { isOptional: true } as the second parameter:

import {injectable, injectAll} from "tsyringe";

@injectable()
class Foo {
  constructor(@inject("Database", { isOptional: true }) private database?: Database) {}
}

injectAll()

Parameter decorator for array parameters where the array contents will come from the container. It will inject an array using the specified injection token to resolve the values.

Usage

import {injectable, injectAll} from "tsyringe";

@injectable()
class Foo {}

@injectable()
class Bar {
  constructor(@injectAll(Foo) fooArray: Foo[]) {
    // ...
  }
}

Optional

By default, @injectAll() throws an exception if no registrations were found. If you want to return an empty array, you can pass this options { isOptional: true } as the second parameter:

import {injectable, injectAll} from "tsyringe";

@injectable()
class Bar {
  constructor(@injectAll(Foo, { isOptional: true }) fooArray: Foo[]) {
    // ...
  }
}

injectWithTransform()

Parameter decorator which allows for a transformer object to take an action on the resolved object before returning the result.

class FeatureFlags {
  public getFlagValue(flagName: string): boolean {
    // ...
  }
}

class Foo() {}

class FeatureFlagsTransformer implements Transform<FeatureFlags, boolean> {
  public transform(flags: FeatureFlags, flag: string) {
    return flags.getFlagValue(flag);
  }
}

@injectable()
class MyComponent(foo: Foo, @injectWithTransform(FeatureFlags, FeatureFlagsTransformer, "IsBlahEnabled") blahEnabled: boolean){
  // ...
}

injectAllWithTransform()

This parameter decorator allows for array contents to be passed through a transformer. The transformer can return any type, so this can be used to map or fold an array.

@injectable()
class Foo {
  public value;
}

class FooTransform implements Transform<Foo[], string[]>{
  public transform(foos: Foo[]): string[]{
    return foos.map(f => f.value));
  }
}

@injectable()
class Bar {
  constructor(@injectAllWithTransform(Foo, FooTransform) stringArray: string[]) {
    // ...
  }
}

scoped()

Class decorator factory that registers the class as a scoped dependency within the global container.

Available scopes

• Transient
  • The default registration scope, a new instance will be created with each resolve
• Singleton
  • Each resolve will return the same instance (including resolves from child containers)
• ResolutionScoped
  • The same instance will be resolved for each resolution of this dependency during a single resolution chain
• ContainerScoped
  • The dependency container will return the same instance each time a resolution for this dependency is requested. This is similar to being a singleton, however if a child container is made, that child container will resolve an instance unique to it.

Usage

@scoped(Lifecycle.ContainerScoped)
class Foo {}

Container

The general principle behind Inversion of Control (IoC) containers is you give the container a token, and in exchange you get an instance/value. Our container automatically figures out the tokens most of the time, with 2 major exceptions, interfaces and non-class types, which require the @inject() decorator to be used on the constructor parameter to be injected (see above).

In order for your decorated classes to be used, they need to be registered with the container. Registrations take the form of a Token/Provider pair, so we need to take a brief diversion to discuss tokens and providers.

Injection Token

A token may be either a string, a symbol, a class constructor, or a instance of DelayedConstructor.

type InjectionToken<T = any> =
  | constructor<T>
  | DelayedConstructor<T>
  | string
  | symbol;

Providers

Our container has the notion of a provider. A provider is registered with the DI container and provides the container the information needed to resolve an instance for a given token. In our implementation, we have the following 4 provider types:

Class Provider

{
  token: InjectionToken<T>;
  useClass: constructor<T>;
}

This provider is used to resolve classes by their constructor. When registering a class provider you can simply use the constructor itself, unless of course you're making an alias (a class provider where the token isn't the class itself).

Value Provider

{
  token: InjectionToken<T>;
  useValue: T
}

This provider is used to resolve a token to a given value. This is useful for registering constants, or things that have a already bee