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A dependency injection framework for Javascript, inspired by Guice by Google.

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# diska

A lightweight DI framework in Javascript, inspired by Guice by Google.

## Information on Babel 6

Babel 6 doesn't support decorators, which is an important part of diska.
There is a Babel plugin that provides support for legacy decorators, which works the same way they did in Babel 5.
This plugig works with diska, and it is recommended until Babel 6 supports decorators officially.
https://www.npmjs.com/package/babel-plugin-transform-decorators-legacy

React Native supports custom babelrc as of 0.20 which makes it easy to add this plugin.

## Information on React Native

RN 0.15 and older uses Babel 5 and diska works out of the box.
RN 0.16-0.19 uses Babel 6, but uses it's own internal babelrc.
To use diska, you need to patch the babelrc file.
It is recommended to upgrade to RN 0.20 or later, and then add `babel-plugin-transform-decorators-legacy`.

## Releases

#### 1.1.4 (2016-02-26)
* Removed .babelrc from distributed package.

#### 1.1.3 (2016-02-23)
* Bug fix

#### 1.1.2 (2016-02-23)
* New way of creating instances which doesn't create an intermediary object of type Temp. Types are now correct in all ways.
* Added defaultInjector which is empty, and can be used when not needing to bind any types explicitly in a module.

```js
import { defaultInjector } from "diskajs";
import MySweetClass from "./MySweetClass";

let obj = defaultInjector.get(MySweetClass);
```

#### 1.1.1 (2016-01-16)
* Support for injecting the injector

#### 1.1.0 (2015-12-17)
* Support for decorators, @Singleton() and @Inject().

Breaking changes
* Injection based on constructor argument names no longer supported.

#### 1.0.1
* Bug fixes

#### 1.0.0 
* First official release
* Support for injection based on constructor argument names
* Support for static inject()
* Support for modules
* Support for child injectors
* Support for providers

## Installation

```
npm install diskajs --save-dev
```

## Compatibility

* Babel 5.x 
* Babel 6.x (use `babel-plugin-transform-decorators-legacy`)
* React Native 0.15
* React Native 0.16-19 (no support for decorators unless you patch RN's internal babelrc, uses Babel 6)
* React Native 0.20- (add `babel-plugin-transform-decorators-legacy` to babelrc)

## Example code

The tests contain a lot of sample code. They test all features of diska.

You can find most of them here:
https://github.com/mattias800/diskajs/blob/master/test/di/InjectorSpec.js

You can also check out this repository to see how to setup diska with Node or React Native:

https://github.com/mattias800/diskajs-examples

These have not been updated in a while though, and do not use decorators.
Also, they were made for an older version of React Native where Webpack was required for diska to work.
You can use diska in React Native projects without Webpack now.

## Dependency injection

To learn how dependency injection and Guice works, please see the Guice documentation.
All diska documentation assumes that you have previous experience with Guice and DI.
While this is not a clone of Guice, it is inspired by it and anyone who has used Guice
will be instantly familiar with diska.

## Tutorial

First things first; To start injecting, you need an injector.
And to get an injector, you need a module that defines what to inject.

Let's start with an empty module.

```js
import UserFactory from "./UserFactory";
const module = new Module();
const injector = new Injector(module);
const userFactory = injector.get(UserFactory);
```

This should give you an instance of UserFactory.

#### But what does the UserFactory look like?

All classes that are instantiated by diska must either

1. Be decorated with `@Inject()` or
2. have a `static inject()` method that returns a list of types to be injected.

`UserFactory` can look like this:

```js
@Inject()
export default class UserFactory {

createUser() {
    return {};
  }

}
```

The `@Inject()` decorator tells diska that this class can be instantiated, and has no dependencies. 
It creates the instance by running the constructor with no arguments.

#### What if we can't use decorators?

Use `static inject()` instead. It is a method that must return a list of dependency types.
If there are no dependencies, it should just return an empty list.
 
```js
export default class UserFactory {

static inject() {
    return [];     
  }
     
  createUser() {
    return {};
  }

}
```

#### But how do I add a dependency?

To add a dependency, import it, add it to `@Inject` parameters and add a constructor argument.

```js
import UserDecorator from "./UserDecorator";
import {Inject} from "diskajs";

@Inject(UserDecorator)
export default class UserFactory {

userDecorator:UserDecorator;
    
  constructor(userDecorator:UserDecorator) {
    this.userDecorator = userDecorator;
  }
    
  createUser() {
    return this.userDecorator.decorate({});
  }

}
```

If you cannot use decorators, add the dependency to the list returned by `static inject()`.

```js
static inject() {
  return [UserDecorator];     
}
```

Now when diska tries to create an instance, it finds that it needs a `UserDecorator` instance, 
so it creates an instance of it in the same way it is trying to create an instance of `UserDecorator`.

#### What if you have more than one dependency?

Just add more types to the `@Inject(...)` decoration.

```js
import UserDecorator from "./UserDecorator";
import UserTransformer from "./UserTransformer";
import {Inject} from "diskajs";

@Inject(UserDecorator, UserTransformer)
export default class UserFactory {

userDecorator:UserDecorator;
  userTransformer:UserTransformer;
    
  constructor(userDecorator:UserDecorator,
              userTransformer:UserTransformer) {
    this.userDecorator = userDecorator;
    this.userTransformer = userTransformer;
  }
    
  createUser() {
    return this.userDecorator.decorate({});
  }

}
```

The injected dependency instances are passed to the constructor in the same order as they are 
specified in the `@Inject()` decoration.
In this case, the `UserDecorator` instance will be passed as first argument, and `UserTransformer` as the second argument.

If any of these classes have dependencies, diska will try to instantiate them as well.
This is repeated recursively until it has created all dependencies in the object tree, or until it reaches a dependency 
that it cannot create, in which case an exception is thrown.

#### What if I want to inject a very specific instance of an object?

You can do that when binding.

```js
import User from "./User";
let myVerySpecificUser = new User(1);
const module = new Module();
module.bind(User).toInstance(myVerySpecificUser);
```

#### What if we have a mock version of `UserFactory` that we want to use in our tests?

You can bind another type to it. Setup a new module that is used just for tests (are that specific test).

```js
const module = new Module();
module.bind(UserFactory).to(MockedUserFactory);
const injector = new Injector(module);
const userFactory = injector.get(UserFactory);
```

#### What if we want the `UserFactory` to be a singleton, so that we reuse it instead of creating new instances all the time?

Add `@Singleton()` to the class.

```js
import UserDecorator from "./UserDecorator";
import {Inject, Singleton} from "diskajs";

@Inject(UserDecorator)
@Singleton()
export default class UserFactory {

userDecorator:UserDecorator;
    
  constructor(userDecorator:UserDecorator) {
    this.userDecorator = userDecorator;
  }
    
  createUser() {
    return this.userDecorator.decorate({});
  }

}
```

### What if I need the injector to get instances manually?

Just inject it.

```js
import {Inject, Injector} from "diskajs";

@Inject(Injector)
export default class ClassWithInjector {

injector:Injector;

constructor(injector:Injector) {
    this.injector = injector;  
  }
  
}
```

#### What if we want to declare it as singleton in the binding, instead of forcing the class to always be a singleton?

Just add `.asSingleton()` to the binding.
```js
const module = new Module();
module.bind(UserFactory).to(UserFactory).asSingleton();
const injector = new Injector(module);
const userFactory = injector.get(UserFactory);
```

#### ES5

If you are running ES5, you don't have classes. 
Instead, you can use functions and set the `inject` property on the function.

```js
var Grinder = require('./Grinder');

function CoffeeMaker(grinder) {

this.grinder = grinder;
    
  this.brew = function() {
    this.grinder.grind();
    return 'brew';
  }

}

CoffeeMaker.inject = function() {
  return [Grinder];
}
```

### Modules

A module is a configuration that defines what the injector should inject.

```js
const module = new Module();
module.bind(Grinder).to(Grinder);
module.bind(CoffeeMaker).to(CoffeeMaker);
const injector = new Injector(module);
const coffeeMaker = injector.get(CoffeeMaker);
coffeeMaker.brew();
```

In this example we only have one type of Grinder and CoffeeMaker.
Binding a class to itself is optional and we can remove them.

```js
const module = new Module();
const injector = new Injector(module);
const coffeeMaker = injector.get(CoffeeMaker);
coffeeMaker.brew();
```

When there is no binding for that type in th emodul and we try to inject `CoffeeMaker`, 
it will just inject an instance of `CoffeeMaker`.

#### Using multiple modules

The injector constructor can take multiple arguments where all arguments are modules, 
or one argument that is an array of modules.

```js
// One argument that is an array of modules
const module1 = new Module();
const module2 = new Module();
const injector = new Injector([module1, module2]);
```

```js
// Several arguments that are all modules
const module1 = new Module();
const module2 = new Module();
const injector = new Injector(module1, module2);
```

If multiple modules contain binding for the same type, the binding of the first module
in the array or arguments will be used.

#### Unit tests

When testing, you typically create a separate testing module that is used to create instances in your tests.
The injector that is created with that module can then be imported in your test code and used to create instances.

```js
import {testInjector} from 'path/to/testInjector';
import ArrayUtil from 'path/to/ArrayUtil';

const arrayUtil:ArrayUtil = testInjector.get(ArrayUtil);

describe("ArrayUtil", () => {
  it("should ...", () => {
    // expect()...
  });
});
```

If a test requires something specific for that test only, you can create a local module, and a child injector with that module.

```js
import {Injector, Module} from "diskajs";

import {testInjector} from 'path/to/testInjector';
import ArrayUtil from 'path/to/ArrayUtil';
import ArrayUtilMock from 'path/to/ArrayUtilMock';

const localModule = new Module();
module.bind(ArrayUtil).to(ArrayUtilMock);

const localInjector = testInjector.getChildInjector(localModule);

const arrayUtil:ArrayUtil = localInjector.get(ArrayUtil);

// arrayUtil is an ArrayUtilMock instance

describe("ArrayUtil", () => {
  it("should ...", () => {
    // expect()...
  });
});
```

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