The most common place to use dependency injection in angular applications is in controllers. Here is a simple example:
function MyController($location){ // do stuff with the $location service } MyController.$inject = ['$location'];
In this example, the MyController
constructor function takes one argument, the $location
service. Angular is then responsible for supplying the
instance of $location
to the controller when the constructor is instantiated. There are two ways
to cause controller instantiation – by configuring routes with the $location
service, or by
referencing the controller from the HTML template, as follows:
<!doctype html> <html ng-controller="MyController" ng-app> <script src="http://code.angularjs.org/angular.min.js"></script> <body> ... </body> </html>
When angular is instantiating your controller, it needs to know what services, if any, should be
injected (passed in as arguments) into the controller. Since there is no reflection in JavaScript,
we have to supply this information to angular in the form of an additional property on the
controller constructor function called $inject
. Think of it as annotations for JavaScript.
MyController.$inject = ['$location'];
The information in $inject
is then used by the injector
to call the
function with the correct arguments.