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Simple dependency injection with promise support
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dip - Dependency Injector w/ Promise Support

What is it?

dip provides dependency injection with automatic promise resolution, parent/child relationships and factory dependencies

It's very similiar to angular's dependency injector, but works much better with standalone functions and on-the-fly dependencies (for example if you wanted to register a 'request' dependency that resolves to the current http request)

For now unresolved dependencies will resolve to undefined


npm install --save dip


Creating a dependency injector and a function that has dependencies

var DI = require('dip')
var di = new DI({'foo': 'Hello', 'bar': 'World'})

function fn(foo, bar){
    return foo + ', ' + bar + '!'

Basic function call{
     console.log(foo) // foo == 'Hello'


di.register('foo', Q('Hello').delay(1000)){ // called after foo promise resolves (1 second delay)
    console.log(result)  // result == 'Hello, World!'


// Factories can return promises, factories can even be promises themselves (that resolve to functions)
di.factory('greetingWithDate', function(foo){
    return foo +', it is ' + new Date()
    console.log(greetingWithDate) // greetingWithDate = 'Hello, it is Mon Jun 24 2013 12:30:05 GMT-0400 (EDT)

Parent/Child injectors

var child = di.create('baz', 'qux'), baz){
    console.log(foo) // foo == 'Hello'
    console.log(baz) // baz == 'qux'

Mongoose/Express Example with Promises/Factories

di.factory('user', function(user_id){
    return User.findOne({_id: new ObjectId(user_id)})

di.factory('username', function(user){
    return user.username

app.get('/user/:user_id/username', function(req, res, next){
    var rdi = di.create(req.params){
    }).fail(next) // will call next(err) on failure

// Another method
app.get('/user/:user_id/username', function(req, res, next){
      .inject(res.send, ['username'])
      .call(res.send, res)

// Without using inject
app.get('/user/:user_id/username', function(req, res, next){

Manually specifying dependencies

DI.inject(fn, ['foo'])
// When you specify dependencies you can pass additional arguments, only specified dependencies will be resolved
// returns a promise for the result, context, 'Guys', 'more args').then(function(result){
    console.log(result) // result == 'Hello, Guys!'

Creating a resolved function (returns a promise)

var fn = di.resolved(fn)
    console.log(result) // result == 'Hello, World!'

Getting an resolved function (returns the return value)

    console.log(resolvedFN()) // returns 'Hello, World!', no promise!

Manually resolving an array of dependencies

// returns an array of dependencies either from the parameter names or specified manually via DI.inject(fn, arrayOfDependencies)
var deps = DI.inject(fn) // ['foo', 'bar'] 

// returns the parameter names
var deps = DI.params(fn)

// or just specify your own array
var deps = ['foo', 'bar']
di.resolve(deps).spread(function(foo, bar){
    console.log(foo) // foo == 'Hello'
    console.log(bar) // bar == 'World'

For more information read the docs (./docs/index.html) or look at the tests (./tests)

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