AngularJS

One of the features I miss the most in AngularJS is ability to easy unsubscribe event handlers. There is no convenience function opposed to $on, so in order to unsubscribe event, we have to call method returned by $on function

(function () {
    angular.module('app.download', [])
        .controller('downloadCtrl', downloadController);

    function downloadController($scope) {
        // keep the unsubscribe function in local variable
        var afterRenderUnsubscribe = $scope.$on('afterRender', onAfterRender);

        function onAfterRender() {
            console.log('CallingonAfterRender');
            // unsubscribe form event
            afterRenderUnsubscribe();
        }
    }
}());

(function () {

angular.module('app.download', [])

.controller('downloadCtrl', downloadController);

function downloadController($scope) {

// keep the unsubscribe function in local variable

var afterRenderUnsubscribe = $scope.$on('afterRender', onAfterRender);

function onAfterRender() {

console.log('CallingonAfterRender');

// unsubscribe form event

afterRenderUnsubscribe();

}

}());

However in my opinion this approach fails in real life scenarios, because usually we are subscribed to more than one event – thus we have to have multiple local variables for detaching listeners. Fortunately AngularJS provides an easy way to extend existing services with some new functionalities – we can achieve that by using $provide service. This service exposes decorator method, which is able to intercept creation of any service, so we are able to augment it with some new functions. The best moment to call $provide.decorator method is during module configuration, thanks to this approach we are sure that our custom logic is invoked before module is started.

angular.module('app.common', [])
       .config(extendServices);

/*ngInject*/
function extendServices($provide) {
    $provide.decorator('serviceName', function ($delegate) {
     /*some interception logic*/
    });
}

angular.module('app.common', [])

.config(extendServices);

/*ngInject*/

function extendServices($provide) {

$provide.decorator('serviceName', function ($delegate) {

/*some interception logic*/

});

}

In my case I wanted to extend $rootScope with new method $un for unsubscribing events, so I called method decorator with parameter ‘$rootScope’ (note single quotation marks) – this tells Angular that I will be modifying $rootScope service

angular.module('app.common', [])
    .config(extendServices);

/*ngInject*/
function extendServices($provide) {
    $provide.decorator('$rootScope', extendRootScope);
}

/*ngInject*/
function extendRootScope($delegate) {
}

angular.module('app.common', [])

.config(extendServices);

/*ngInject*/

function extendServices($provide) {

$provide.decorator('$rootScope', extendRootScope);

}

/*ngInject*/

function extendRootScope($delegate) {

}

Because I passed ‘$rootScope’ as a first argument of $provide.decorator method, the $delegate parameter in extendRootScope function is actually a $rootScope service. Now having access to the service I can augment it with my custom logic for detaching event handlers.

/*ngInject*/
function extendRootScope($delegate){
    $delegate.$un=function(name,listener){
        var namedListeners=this.$$listeners[name],
            idx;
        if(namedListeners&&(idx=namedListeners.indexOf(listener))>-1){
            namedListeners.splice(idx,1);
        }
    };
    return $delegate;
}

/*ngInject*/

function extendRootScope($delegate){

$delegate.$un=function(name,listener){

var namedListeners=this.$$listeners[name],

idx;

if(namedListeners&&(idx=namedListeners.indexOf(listener))>-1){

namedListeners.splice(idx,1);

}

};

return $delegate;

}

Entire code listing looks then as follows

(function () {
    angular.module('app.common', [])
           .config(extendServices);

    /*ngInject*/
    function extendServices($provide)
    {
        $provide.decorator('$rootScope', extendRootScope);
    }

    /*ngInject*/
    function extendRootScope($delegate)
    {
        $delegate.$un = function (name, listener) {
            var namedListeners = this.$$listeners[name],
                idx;
            if (namedListeners && (idx = namedListeners.indexOf(listener)) > -1) {
                namedListeners.splice(idx, 1);
            }
        };
        return $delegate;
    }
}());

(function () {

angular.module('app.common', [])

.config(extendServices);

/*ngInject*/

function extendServices($provide)

{

$provide.decorator('$rootScope', extendRootScope);

}

/*ngInject*/

function extendRootScope($delegate)

{

$delegate.$un = function (name, listener) {

var namedListeners = this.$$listeners[name],

idx;

if (namedListeners && (idx = namedListeners.indexOf(listener)) > -1) {

namedListeners.splice(idx, 1);

}

};

return $delegate;

}

}());

From now on, you can unsubscribe events handlers simply by calling $un method

(function () {
    angular.module('app.download', ['app.common'])
        .controller('downloadCtrl', downloadController);

    function downloadController($scope) {
        $scope.$on('afterRender', onAfterRender);

        function onAfterRender() {
            console.log('Calling afterRender handler');
            $scope.$un('afterRender', onAfterRender);
        }
    }
}());

(function () {

angular.module('app.download', ['app.common'])

.controller('downloadCtrl', downloadController);

function downloadController($scope) {

$scope.$on('afterRender', onAfterRender);

function onAfterRender() {

console.log('Calling afterRender handler');

$scope.$un('afterRender', onAfterRender);

}

}());

and our listener will react only once

console.log('Broadcasting afterRender event for the first time');
$rootScope.$broadcast('afterRender');
console.log('Broadcasting afterRender event for the second time');
$rootScope.$broadcast('afterRender');

console.log('Broadcasting afterRender event for the first time');

$rootScope.$broadcast('afterRender');

console.log('Broadcasting afterRender event for the second time');

$rootScope.$broadcast('afterRender');

Source code for this post can be found here

There are couple of ways of injecting dependencies into AngularJS components. The most common one is just to specify the dependency name in the function’s argument list

(function() {
    angular
        .module('app')
        .controller('shellCtrl', function ($scope, $http) {
            $scope.title = "Title";
        });
})();

(function() {

angular

.module('app')

.controller('shellCtrl', function ($scope, $http) {

$scope.title = "Title";

});

})();

However this technique fails in real life scenarios, because for production we usually (or rather always) minify and uglify javascript files. Uglify proces renames our variables and due to the fact that dependencies are resolved by name, AngularJS is not able to find appropriate services, directives etc. To overcome this limitation, we can enclose our function definition into an array, and specify dependencies as a string literals. Our original code becomes then

(function () {
    angular.module('app')
           .controller('shellCtrl', ['$scope', '$http', function ($scope, $http) {
               $scope.title = "Title";
           }]);
})();

(function () {

angular.module('app')

.controller('shellCtrl', ['$scope', '$http', function ($scope, $http) {

$scope.title = "Title";

}]);

})();

Although this works fine even after minifying and uglifiyng js files, for me this code is hard to read. That is why I like to use yet another technique. This technique leverages variable hoisting and $inject property

(function(){
    angular.module('app')
           .controller('shellCtrl',shellController);

    shellController.$inject=['$scope','$http'];

    function shellController($scope,$http){
        $scope.title='title';
    }
})();

(function(){

angular.module('app')

.controller('shellCtrl',shellController);

shellController.$inject=['$scope','$http'];

function shellController($scope,$http){

$scope.title='title';

}

})();

As You can see I extracted controller function into separate variable “shellController” and listed all necessary dependencies in $inject array

shellController.$inject= ['$scope','$http']

1	shellController.$inject= ['$scope','$http']

It is even possible to enhance a bit this example and make it a little less error prone. With the current implementation we have to make sure that order of properties in $inject array is the same as in function declaration. It is easy to keep track of that if we have just a couple of dependencies, but it might be a bit of a pain if we start to add, remove or edit them. Fortunately we can automate this task and basically autogenerate $inject array. In order to do that I like to use Gulp (although it is also possible to use Grunt). First of all we have to install Gulp. There is great tutorial how to do that in here https://github.com/gulpjs/gulp/blob/master/docs/getting-started.md Having Gulp on board we have to install additional packages: gulp-rename and gulp-ng-annotate. In order to do that type into command line

npm install gulp-ng-annotate --save-dev
npm install gulp-rename --save-dev

1 2	npm install gulp-ng-annotate --save-dev npm install gulp-rename --save-dev

Now we can create gulp.js file which should look more or less like that

var rename = require('gulp-rename'),
    ngAnnotate = require('gulp-ng-annotate');

gulp.task('annotate', function () { //create new task 'annotate'
    return gulp.src('app/layout/controllers/shellController.js') //select files to process
        .pipe(ngAnnotate()) // add angularjs dependeny injection annotation
        .pipe(rename('app.all.js')) //rename in-memory stream to app.all.js
        .pipe(gulp.dest('.build'));//save stream to new location
})

var rename = require('gulp-rename'),

ngAnnotate = require('gulp-ng-annotate');

gulp.task('annotate', function () { //create new task 'annotate'

return gulp.src('app/layout/controllers/shellController.js') //select files to process

.pipe(ngAnnotate()) // add angularjs dependeny injection annotation

.pipe(rename('app.all.js')) //rename in-memory stream to app.all.js

.pipe(gulp.dest('.build'));//save stream to new location

})

We can run this task typing into command line

gulp annotate

1	gulp annotate

And as a result our original code (notice lack of dependeny annotations – no $inject arrray)

(function() {
    angular.module('app')
           .controller('shellCtrl', shellController);

    function shellController($scope, $http) {
        $scope.title = 'title';
    }
})();

(function() {

angular.module('app')

.controller('shellCtrl', shellController);

function shellController($scope, $http) {

$scope.title = 'title';

}

})();

Will be transformed into

(function(){
    angular.module('app')
           .controller('shellCtrl',shellController);

    function shellController($scope,$http){
    }
    
shellController.$inject=["$scope","$http"];
})();

(function(){

angular.module('app')

.controller('shellCtrl',shellController);

function shellController($scope,$http){

}

shellController.$inject=["$scope","$http"];

})();

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AngularJS – extending existing services using decorator

AngularJS – dependency injection