Angular - Injector & Module / Service

Overview

• Injector is a service locator. There's a single injector per Angular application.

• Injector looks up an object by its name, and keeps an internal caches of all objects. Repeated calls to get the same object name result in the same instance.

• If the object does not exit, injector will asks the instance factory to create a new one.

• So, a module is the way to configure the injector's instance factory, known as a provider.

Documents

Injector

$injector is used to retrive object instances as defined by provider, instantiate types, invoke methods, and load modules.

var $injector = angular.injector();

expect($injector.get('$injector')).toBe($injector);

expect($injector.invoke(function($injector){
	return $injector;
}).toBe($injector);

Annotation Strategy

Javascript does not have annotations, annotations are needed for dependency injection. But some minified/obfuscated tool will change the name of arguments, so we need some ways to make valid annotations.

// inferred (only works is code not minified/obfuscated)
$inject.invoke(function(serviceA){});

// annotated
function explicit(serviceA){};
explicit.$inject = ['serviceA'];
$inject.invoke(explicit);

// inline
$inject.invoke(['serviceA', function(serviceA){}]);

Module

The angular.module is a global place for creating and registering Angular modules.

All Modules (angular core or 3rd party) that should be available to an application must be registered using this mechanism.