InversifyJS

A lightweight IoC container written in TypeScript.

About

InversifyJS is a lightweight (4KB) pico inversion of control (IoC) container for TypeScript and JavaScript apps. A pico IoC container uses a class constructor to identify and inject its dependencies. InversifyJS has a friendly API and encourage the usage of the best OOP and IoC practices.

Motivation

JavaScript applications are becoming larger and larger day after day. InversifyJS has been designed to allow JavaScript developers to write code that adheres to the SOLID principles.

Philosophy

InversifyJS has been developed with 3 main goals:

Allow JavaScript developers to write code that adheres to the SOLID principles.
Facilitate and encourage the adherence to the best OOP and IoC practices.
Add as little runtime overhead as possible.

Installation

You can get the latest release and the type definitions using npm:

npm install [email protected] --save

Note: We have decided to drop support for bower and tsd.

The InversifyJS type definitions are included in the npm package:

/// <reference path="node_modules/inversify/type_definitions/inversify/inversify.d.ts" />

Note: InversifyJS requires a modern JavaScript engine with support for the Promise, Reflect (with metadata) and Proxy objects. If your environment don't support one of these you will need to import a shim or polypill. Check out the Environment support and polyfills page in the wiki to learn more.

The Basics (TypeScript)

Let’s take a look to the basic usage and APIs of InversifyJS with TypeScript:

Step 1: Declare your interfaces

Our goal is to write code that adheres to the dependency inversion principle. This means that we should "depend upon Abstractions and do not depend upon concretions". Let's start by declaring some interfaces (abstractions).

interface INinja {
    fight(): string;
    sneak(): string;
}

interface IKatana {
    hit(): string;
}

interface IShuriken {
    throw();
}

Step 2: Implement the interfaces and declare dependencies using the `@injectable` decorator

Let's continue by declaring some classes (concretions). The classes are implementations of the interfaces that we just declared.

import { injectable } from "inversify";

class Katana implements IKatana {
    public hit() {
        return "cut!";
    }
}

class Shuriken implements IShuriken {
    public throw() {
        return "hit!";
    }
}

@injectable("IKatana", "IShuriken")
class Ninja implements INinja {

    private _katana: IKatana;
    private _shuriken: IShuriken;

    public constructor(katana: IKatana, shuriken: IShuriken) {
        this._katana = katana;
        this._shuriken = shuriken;
    }

    public fight() { return this._katana.hit(); };
    public sneak() { return this._shuriken.throw(); };

}

Step 3: Create and configure a Kernel

We recommend to do this in a file named inversify.config.ts. This is the only place in which there is some coupling. In the rest of your application your classes should be free of references to other classes.

import { Kernel } from "inversify";

import { Ninja } from "./entities/ninja";
import { Katana } from "./entities/katana";
import { Shuriken} from "./entities/shuriken";

var kernel = new Kernel();
kernel.bind<INinja>("INinja").to(Ninja);
kernel.bind<IKatana>("IKatana").to(Katana);
kernel.bind<IShuriken>("IShuriken").to(Shuriken);

export default kernel;

Step 4: Resolve dependencies

You can use the method get<T> from the Kernel class to resolve a dependency. Remember that you should do this only in your composition root to avoid the service locator anti-pattern.

import kernel = from "./inversify.config";

var ninja = kernel.get<INinja>("INinja");

expect(ninja.fight()).eql("cut!"); // true
expect(ninja.sneak()).eql("hit!"); // true

As we can see the IKatana and IShuriken were successfully resolved and injected into Ninja.

The Basics (JavaScript)

It is recommended to use TypeScript for the best development experience but you can use plain JavaScript if you preffer it. The following code snippet implements the previous example without TypeScript in Node.js v5.71:

var inversify = require("inversify");
require("reflect-metadata");

var TYPES = {
    Ninja: "Ninja",
    Katana: "Katana",
    Shuriken: "Shuriken"
};

class Katana {
    hit() {
        return "cut!";
    }
}

class Shuriken {
    throw() {
        return "hit!";
    }
}

class Ninja {
    constructor(katana, shuriken) {
        this._katana = katana;
        this._shuriken = shuriken;
    }
    fight() { return this._katana.hit(); };
    sneak() { return this._shuriken.throw(); };
}

// Declare as injectable and its dependencies
inversify.injectable(TYPES.Katana, TYPES.Shuriken)(Ninja);

// Declare bindings
var kernel = new inversify.Kernel();
kernel.bind(TYPES.Ninja).to(Ninja);
kernel.bind(TYPES.Katana).to(Katana);
kernel.bind(TYPES.Shuriken).to(Shuriken);

// Resolve dependencies
var ninja = kernel.get(TYPES.Ninja);
return ninja;

Features (v2.0.0-alpha.6)

Let's take a look to the InversifyJS features!

Declaring kernel modules

Kernel modules can help you to manage the complexity of your bindings in very large applications.

let warriors: IKernelModule = (k: IKernel) => {
    k.bind<INinja>("INinja").to(Ninja);
};

let weapons: IKernelModule = (k: IKernel) => {
    k.bind<IKatana>("IKatana").to(Katana).inTransientScope();
    k.bind<IShuriken>("IShuriken").to(Shuriken).inSingletonScope();
};

kernel = new Kernel();
kernel.load(warriors, weapons);

Controlling the scope of the dependencies

InversifyJS uses transient scope by default but you can also use singleton scope:

kernel.bind<IShuriken>("IShuriken").to(Shuriken).inTransientScope(); // Default
kernel.bind<IShuriken>("IShuriken").to(Shuriken).inSingletonScope();

Injecting a value

Binds an abstraction to a constant value.

kernel.bind<IKatana>("IKatana").toValue(new Katana());

Injecting a class constructor

Binds an abstraction to a class constructor.

@injectable("IKatana", "IShuriken")
class Ninja implements INinja {

    private _katana: IKatana;
    private _shuriken: IShuriken;

    public constructor(Katana: INewable<IKatana>, shuriken: IShuriken) {
        this._katana = new Katana();
        this._shuriken = shuriken;
    }

    public fight() { return this._katana.hit(); };
    public sneak() { return this._shuriken.throw(); };

}

kernel.bind<INewable<IKatana>>("INewable<IKatana>").toConstructor<IKatana>(Katana);

Injecting a Factory

Binds an abstraction to a user defined Factory.

@injectable("IKatana", "IShuriken")
class Ninja implements INinja {

    private _katana: IKatana;
    private _shuriken: IShuriken;

    public constructor(katanaFactory: IFactory<IKatana>, shuriken: IShuriken) {
        this._katana = katanaFactory();
        this._shuriken = shuriken;
    }

    public fight() { return this._katana.hit(); };
    public sneak() { return this._shuriken.throw(); };

}

kernel.bind<IFactory<IKatana>>("IFactory<IKatana>").toFactory<IKatana>((context) => {
    return () => {
        return context.kernel.get<IKatana>("IKatana");
    };
});

Auto factory

Binds an abstraction to a auto-generated Factory.

@injectable("IKatana", "IShuriken")
class Ninja implements INinja {

    private _katana: IKatana;
    private _shuriken: IShuriken;

    public constructor(katanaFactory: IFactory<IKatana>, shuriken: IShuriken) {
        this._katana = katanaFactory();
        this._shuriken = shuriken;
    }

    public fight() { return this._katana.hit(); };
    public sneak() { return this._shuriken.throw(); };

}

kernel.bind<IFactory<IKatana>>("IFactory<IKatana>").toAutoFactory<IKatana>();

Injecting a Provider (asynchronous Factory)

Binds an abstraction to a Provider. A provider is an asynchronous factory, this is useful when dealing with asynchronous I/O operations.

@injectable("IKatana", "IShuriken")
class Ninja implements INinja {

    public katana: IKatana;
    public shuriken: IShuriken;
    public katanaProvider: IProvider<IKatana>;

    public constructor(katanaProvider: IProvider<IKatana>, shuriken: IShuriken) {
        this.katanaProvider = katanaProvider;
        this.katana= null;
        this.shuriken = shuriken;
    }

    public fight() { return this._katana.hit(); };
    public sneak() { return this._shuriken.throw(); };

}

var ninja = kernel.get<INinja>("INinja");

ninja.katanaProvider()
     .then((katana) => { ninja.katana = katana; })
     .catch((e) => { console.log(e); });

kernel.bind<IProvider<IKatana>>("IProvider<IKatana>").toProvider<IKatana>((context) => {
    return () => {
        return new Promise<IKatana>((resolve) => {
            let katana = context.kernel.get<IKatana>("IKatana");
            resolve(katana);
        });
    };
});

Activation handler

It is possible to add an activation handler for a type. The activation handler is invoked after a dependency has been resolved and before it is added to the cache (if singleton) and injected. This is useful to keep our dependencies agnostic of the implementation of crosscutting concerns like caching or logging. The following example uses a proxy to incercept one of the methods (use) of a dependency (IKatana).

interface IKatana {
    use: () => void;
}

class Katana implements IKatana {
    public use() {
        console.log("Used Katana!");
    }
}

interface INinja {
    katana: IKatana;
}

@injectable("IKatana")
class Ninja implements INinja {
    public katana: IKatana;
    public constructor(katana: IKatana) {
        this.katana = katana;
    }
}

kernel.bind<INinja>("INinja").to(Ninja);

kernel.bind<IKatana>("IKatana").to(Katana).onActivation((context, katana) => {
    let handler = {
        apply: function(target, thisArgument, argumentsList) {
            console.log(`Starting: ${new Date().getTime()}`);
            let result = target.apply(thisArgument, argumentsList);
            console.log(`Finished: ${new Date().getTime()}`);
            return result;
        }
    };
    katana.use = new Proxy(katana.use, handler);
    return katana;
});

let ninja = kernelget<INinja>();
ninja.katana.use();
> Starting: 1457895135761
> Used Katana!
> Finished: 1457895135762

Middleware

InversifyJS performs 3 mandatory operations before resolving a dependency:

Annotation
Planning
Middleware (optional)
Resolution
Activation (optional)

In some cases there will be some additional operations (middleware & activation).

If we have configured some Middleware it will be executed just before the resolution phase takes place.

Middleware can be used to implement powerful development tools. This kind of tools will help developers to identify problems during the development process.

function logger(next: (context: IContext) => any) {
    return (context: IContext) => {
        let result = next(context);
        console.log("CONTEXT: ", context);
        console.log("RESULT: ", result);
        return result;
    };
};

function devTools(next: (context: IContext) => any) {
    return (context: IContext) => {
        let result = next(context);
        let _window: any = window;
        let __inversify_devtools__ = _window.__inversify_devtools__;
        if (__inversify_devtools__ !== undefined) { __inversify_devtools__.log(context, result); }
        return result;
    };
};

Now that we have declared two middlewares we can create a new Kernel and use its applyMiddleware method to apply them,

interface INinja {}
class Ninja implements INinja {}

let kernel = new Kernel();
kernel.bind<INinja>("INinja").to(Ninja);

kernel.applyMiddleware(logger, devTools);

The logger middleware will log in console the context and result. The crashReporter middleware is not invoked because __inversify_devtools__ is undefined.

let ninja = kernel.get<INinja>("INinja");
> CONTEXT:  Context {
  kernel: 
   Kernel {
     _planner: Planner {},
     _resolver: Resolver {},
     _bindingDictionary: Lookup { _dictionary: [Object] },
     _middleware: [Function] },
  plan: 
   Plan {
     parentContext: [Circular],
     rootRequest: 
      Request {
        guid: '9b5d5435-d784-c9e2-c666-5b5e2cf98221',
        service: 'INinja',
        parentContext: [Circular],
        parentRequest: null,
        target: null,
        childRequests: [],
        bindings: [Object] } } }
> RESULT:  Ninja {}

Multi-injection

We can use multi-injection When two or more concretions have been bound to the an abstraction. Notice how an array of IWeapon is injected into the Ninja class via its constructor:

interface IWeapon {
    name: string;
}

class Katana implements IWeapon {
    public name = "Katana";
}
class Shuriken implements IWeapon {
    public name = "Shuriken";
}

interface INinja {
    katana: IWeapon;
    shuriken: IWeapon;
}

@injectable("IWeapon[]")
class Ninja implements INinja {
    public katana: IWeapon;
    public shuriken: IWeapon;
    public constructor(weapons: IWeapon[]) {
        this.katana = weapons[0];
        this.shuriken = weapons[1];
    }
}

We are binding Katana and Shuriken to IWeapon:

kernel.bind<INinja>("INinja").to(Ninja);
kernel.bind<IWeapon>("IWeapon").to(Katana);
kernel.bind<IWeapon>("IWeapon").to(Shuriken);

Tagged bindings

We can use tagged bindings to fix AMBIGUOUS_MATCH errors when two or more concretions have been bound to the an abstraction. Notice how the constructor arguments of the Ninja class have been annotated using the @tagged decorator:

interface IWeapon {}
class Katana implements IWeapon { }
class Shuriken implements IWeapon {}

interface INinja {
    katana: IWeapon;
    shuriken: IWeapon;
}

@injectable("IWeapon", "IWeapon")
class Ninja implements INinja {
    public katana: IWeapon;
    public shuriken: IWeapon;
    public constructor(
        @tagged("canThrow", false) katana: IWeapon,
        @tagged("canThrow", true) shuriken: IWeapon
    ) {
        this.katana = katana;
        this.shuriken = shuriken;
    }
}

We are binding Katana and Shuriken to IWeapon but a whenTargetTagged constraint is added to avoid AMBIGUOUS_MATCH errors:

kernel.bind<INinja>(ninjaId).to(Ninja);
kernel.bind<IWeapon>(weaponId).to(Katana).whenTargetTagged("canThrow", false);
kernel.bind<IWeapon>(weaponId).to(Shuriken).whenTargetTagged("canThrow", true);

Create your own tag decorators

Creating your own decorators is really simple:

let throwable = tagged("canThrow", true);
let notThrowable = tagged("canThrow", false);

@injectable("IWeapon", "IWeapon")
class Ninja implements INinja {
    public katana: IWeapon;
    public shuriken: IWeapon;
    public constructor(
        @notThrowable katana: IWeapon,
        @throwable shuriken: IWeapon
    ) {
        this.katana = katana;
        this.shuriken = shuriken;
    }
}

Named bindings

We can use named bindings to fix AMBIGUOUS_MATCH errors when two or more concretions have been bound to the an abstraction. Notice how the constructor arguments of the Ninja class have been annotated using the @named decorator:

interface IWeapon {}
class Katana implements IWeapon { }
class Shuriken implements IWeapon {}

interface INinja {
    katana: IWeapon;
    shuriken: IWeapon;
}

@injectable("IWeapon", "IWeapon")
class Ninja implements INinja {
    public katana: IWeapon;
    public shuriken: IWeapon;
    public constructor(
        @named("strong")katana: IWeapon,
        @named("weak") shuriken: IWeapon
    ) {
        this.katana = katana;
        this.shuriken = shuriken;
    }
}

We are binding Katana and Shuriken to IWeapon but a whenTargetNamed constraint is added to avoid AMBIGUOUS_MATCH errors:

kernel.bind<INinja>("INinja").to(Ninja);
kernel.bind<IWeapon>("IWeapon").to(Katana).whenTargetNamed("strong");
kernel.bind<IWeapon>("IWeapon").to(Shuriken).whenTargetNamed("weak");

Contextual bindings & @paramNames

The @paramNames decorator is used to access the names of the constructor arguments from a contextual constraint even when the code is compressed. The constructor(katana, shuriken) { ... becomes constructor(a, b) { ... after compression but thanks to @paramNames we can still refer to the design-time names katana and shuriken.

interface IWeapon {}
class Katana implements IWeapon { }
class Shuriken implements IWeapon {}

interface INinja {
    katana: IWeapon;
    shuriken: IWeapon;
}

@injectable("IWeapon", "IWeapon")
@paramNames("katana","shuriken")
class Ninja implements INinja {
    public katana: IWeapon;
    public shuriken: IWeapon;
    public constructor(
        katana: IWeapon,
        shuriken: IWeapon
    ) {
        this.katana = katana;
        this.shuriken = shuriken;
    }
}

We are binding Katana and Shuriken to IWeapon but a custom when constraint is added to avoid AMBIGUOUS_MATCH errors:

kernel.bind<INinja>(ninjaId).to(Ninja);

kernel.bind<IWeapon>("IWeapon").to(Katana).when((request: IRequest) => {
    return request.target.name.equals("katana");
});

kernel.bind<IWeapon>("IWeapon").to(Shuriken).when((request: IRequest) => {
    return request.target.name.equals("shuriken");
});

The target fields implement the IQueryableString interface to help you to create your custom constraints:

interface IQueryableString {
  startsWith(searchString: string): boolean;
  endsWith(searchString: string): boolean;
  contains(searchString: string): boolean;
  equals(compareString: string): boolean;
  value(): string;
}

We have included some helpers to facilitate the creation of custom constraints:

import { Kernel, traverseAncerstors, taggedConstraint, namedConstraint, typeConstraint } from "inversify";

let whenParentNamedCanThrowConstraint = (request: IRequest) => {
    return namedConstraint("canThrow")(request.parentRequest);
};

let whenAnyAncestorIsConstraint = (request: IRequest) => {
    return traverseAncerstors(request, typeConstraint(Ninja));
};

let whenAnyAncestorTaggedConstraint = (request: IRequest) => {
    return traverseAncerstors(request, taggedConstraint("canThrow")(true));
};

The InversifyJS fluent syntax for bindings includes some already implemented common contextual constraints:

interface IBindingWhenSyntax<T> {
    when(constraint: (request: IRequest) => boolean): IBindingOnSyntax<T>;
    whenTargetNamed(name: string): IBindingOnSyntax<T>;
    whenTargetTagged(tag: string, value: any): IBindingOnSyntax<T>;
    whenInjectedInto(parent: (Function|string)): IBindingOnSyntax<T>;
    whenParentNamed(name: string): IBindingOnSyntax<T>;
    whenParentTagged(tag: string, value: any): IBindingOnSyntax<T>;
    whenAnyAncestorIs(ancestor: (Function|string)): IBindingOnSyntax<T>;
    whenNoAncestorIs(ancestor: (Function|string)): IBindingOnSyntax<T>;
    whenAnyAncestorNamed(name: string): IBindingOnSyntax<T>;
    whenAnyAncestorTagged(tag: string, value: any): IBindingOnSyntax<T>;
    whenNoAncestorNamed(name: string): IBindingOnSyntax<T>;
    whenNoAncestorTagged(tag: string, value: any): IBindingOnSyntax<T>;
    whenAnyAncestorMatches(constraint: (request: IRequest) => boolean): IBindingOnSyntax<T>;
    whenNoAncestorMatches(constraint: (request: IRequest) => boolean): IBindingOnSyntax<T>;
}

Circular dependencies

InversifyJS is able to identify circular dependencies and will throw an exception to help you to identify the location of the problem if a circular dependency is detected:

Error: Circular dependency found between services: IKatana and INinja

Plese refer to the wiki for additional details.

Live demo & examples

You can try InversifyJS online at tonicdev.com. Some integration examples are available in the official examples repository.

Testimonies

Nate Kohari - Author of Ninject

"Ninject author here. Nice work! I've taken a couple shots at creating DI frameworks for JavaScript and TypeScript, but the lack of RTTI really hinders things. The ES7 metadata gets us part of the way there (as you've discovered). Keep up the great work!"

Support

If you are experience any kind of issues we will be happy to help. You can report an issue using the issues page or the chat. You can also ask questions at Stack overflow using the inversifyjs tag.

If you want to share your thoughts with the development team or join us you will be able to do so using the official the mailing list. You can check out the development wiki and browse the documented source code to learn more about InversifyJS internals.

License

License under the MIT License (MIT)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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