node-di

Simple AngularJS inspired DI container for node.js

Getting started

Installation

npm install node-di-container

Example

var di = require('node-di-container');

// Some app-specific configuration
var config = require('./config');

// Creates an UserRepository based on the configuration
var UserRepositoryProvider = require('./userRepositoryProvider');

// Uses an UserRepository
var UserManager = require('./userManager');

// Registering the dependencies
var container = di.container()
    .value('config', config)
    .service('userRepositoryProvider', UserRepositoryProvider)
    .factory('userRepository', function(userRepositoryProvider) {
        return userRepositoryProvider.getRepository();
    })
    .service('userManager', UserManager);

var injector = di.injector(container);

// Invoking a function with some dependencies
injector.invoke(function (userManager) {
    ...
});

Basic concepts

Creating a DI container

The dependency container is the central repository where the dependencies are stored and later resolved from.

To create a DI container:

var di = require('node-di-container');

var container = di.container();

To create a DI container that caches the resolved dependencies:

var container = di.cacheableContainer();

Containers can be chained, creating scopes that help better organize dependencies:

// Register some global dependencies that will be available to all consumers ...
var global = di.container();

// The scoped container 'sees' its own dependencies and those registered on the parent container (global). All dependencies registered on this container are not available to the parent container though.
var scoped = di.container(global);

// One more level of isolation ...
var local = di.container(scoped);

Resolving dependencies always starts from the current container and moving up the chain of parent containers up until it is resolved or there the top most container is reached. Parent containers have no access to the child containers.

Using multiple levels of containers allows parent dependencies to be overridden without actually breaking the parent container and its consumers. To override a parent dependency simply register the new one using the same key.

Registering dependencies

Dependencies are registered and later resolved by a key. The key is a string that uniquely identifies the dependency in the context of the container.

Depending on how the dependencies are registered there are

Values

Values can be any valid JavaScript object and are resolved to the value itself:

container.value('myVal', 123);

Services

Services are defined by a constructor function. This dependency resolves to the result of the constructor function - usually an object instance.

container.service('myService', MyService);

The constructor function itself may have dependencies that will be resolved before the invocation. For more information how the define dependencies see Dependency annotation.

Factory

This dependency resolves to the result of the factory function.

container.factory('z', function(x, y){
    return (x + y);
});

The function itself may have dependencies that will be resolved on invocation. For more information how the define dependencies see Dependency annotation.

Dependency annotation

Functions with dependencies are invoked vie the injector. These functions need to be annotated so that the injector knows what dependencies to inject into the function.

There are three ways of annotating functions:

• Implicitly from the function parameters names

function f(foo, bar) {
    ...
}

• Using the $inject annotation

function f(arg1, arg2) {
    // arg1 is resolved to foo
    // arg2 is resolved to bar
}

f.$inject = ['foo', 'bar'];

• Using the inline array annotation:

When registering a dependency:

container.service('myService', ['foo', 'bar', MyService]);

container.service('myService', ['foo', 'bar', MyService]);

Invoking a function:

injector.invoke(['foo', 'bar', f])

injector.createInstance(['foo', 'bar', MyObject]);

Resolving dependencies

To invoke a function or create an object instance with dependencies use an injector:

var di = require('node-di-container');
var container = di.container()
                    .value('foo', 1)
                    .value('bar', 2);

var injector = di.injector(container);

For more information how the define dependencies see Dependency annotation.

Invoking a function with dependencies

function foo(foo, bar) {
    return (foo + bar);
}

var result = injector.invoke(foo);

Invoking a constructor function with dependencies

function MyService(foo, bar) {
    ...
}

var myService = injector.createInstance(MyService);

Resolving dependencies by key

Sometimes it is convenient to simply get any dependency like this:

var config = injector.get('config');

API

Top-level API

di

di is the entry point to the node-di-container library:

var di = require('node-di-container');

di.container([parentContainer])

Creates a dependency container.

Parameters:

• parentContainer: (optional)

Returns:

• container

di.cacheableContainer([parentContainer])

Creates a dependency container that cache the dependencies registered as a service or factory.

Parameters:

• parentContainer: (optional)

Returns:

• container

di.injector(container)

Parameters:

• container: the dependency container to resolve the dependencies from.

Returns:

• injector.

Container API

The object created from di.container() or di.cacheableContainer();

container.value(key, value)

Parameters:

• key (String): a string value that uniquely identifies the dependency in this container;
• value (Any): the value this dependency is resolved to.

Returns

• the container object

container.service(key, constructor)

Parameters:

• key (String): a string value that uniquely identifies the dependency in this container;
• constuctor (Function|Array): the constructor function to be invoked on resolving the dependency. The function can have dependencies itself that will be resolved prior to its invocation. For more information on how to annotate a function with dependencies please see Dependency annotation.

Returns

• the container object

container.factory(key, fn)

Parameters:

• key (String): a string value that uniquely identifies the dependency in this container;
• fn (Function|Array): the function to be invoked on resolving the dependency. The function can have dependencies itself that will be resolved prior to its invocation. For more information on how to annotate a function with dependencies please see Dependency annotation.

Returns

• the container object.

container.resolve(key)

Returns the resolved dependency by the given key.

Parameters

• key (String): the key of the dependency to be resolved.

Returns

• the resolved dependency.

Example

var config = container.get('config');

Injector API

The object created from di.injector().

injector.invoke(fn)

Parameters

• fn (Function|Array): the function to be invoked. For more information on how to annotate a function with dependencies please see Dependency annotation.

Returns

• the result of the invocation of the given function fn

Notes

Actual function invocation:

fn.apply(null, [dependencies])

injector.createInstance(constructor)

Parameters

• constructor (Function|Array): the constructor function to be invoked. For more information on how to annotate a function with dependencies please see Dependency annotation.

Returns

• the result of the invocation of the given constructor function constructor.

Notes

Objects are created with Object.create() like this:

var obj = Object.create(constructor.prototype);
constructor.apply(obj, [dependencies]);

injector.get(key)

Returns the resolved dependency by the given key.

Parameters

• key (string): the key of the dependency to be resolved.

Returns

• the resolved dependency.

Notes

This is similar to container.resolve(key).

Example

var config = injector.get('config');