Angular.js, how to pass value from one component to any other

The best solution is to move $scope.isActive to a new 'root' component that contains both 'component A' and 'component B'. Then you can pass / modify its value using input/output bindings in the 'component A' and 'component B' definitions like:

component A definition:

angular.module('app').component('componentA', {    
    templateUrl: 'component-A.html',                 
    bindings: {
       isActive: "<", // use to bind property as component input
       isActiveChanged: "&" // use to bind a METHOD that changes the property in the root component controller
    }
});

component A template (component-A.html):

<img 
   src="res/large-loading.gif" 
   ng-if="!$ctrl.isActive" 
   ng-click="$ctrl.isActiveChanged({isActive: !$ctrl.isActive})"/>

component B definition:

angular.module('app').component('componentB', {    
    template: 'component-B.html',                 
    bindings: {
       isActive: "<", // use to bind property as component input
       isActiveChanged: "&" // use to bind a METHOD that changes the property in the root component controller
    }
});

component B template (component-B.html):

<img 
   src="res/large-loading.gif" 
   ng-if="!$ctrl.isActive" 
   ng-click="$ctrl.isActiveChanged({isActive: !$ctrl.isActive})"/>

root component definition:

angular.module('app').component('root', {    
    templateUrl: 'root-component-view.html', ,                 
    controller: 'RootComponentCtrl'
});

root component controller:

angular.module('app').controller('RootComponentCtrl', ['$scope', function($scope) {
   // INPUT: This property is shared with both 'component A' and 'component B'
   $scope.isActive = true; 
   // OUTPUT: This method is shared with both 'component A' and 'component B' and can be called from both in order to change the value of $scope.isActive in the RootComponentCtrl
   $scope.isActiveChanged(isActive) {
      $scope.isActive = isActive;
   };
}]);

root-component-view.html template:

<div>
   <component-a 
      is-active="isActive" 
      is-active-changed="isActiveChanged(isActive)"
   ></component-a>
   <component-b 
      is-active="isActive" 
      is-active-changed="isActiveChanged(isActive)"
   ></component-b>
</div>

Notice that binded properties are accessed in the component view/template using the '$ctrl' object like '$ctrl.isActive' as opposed to simply using 'isActive' which refers to the component's $scope.isActive property in the component controller.

To resume: The shared property is set in the root component controller using:

$scope.isActive = true;

The shared property can be seen in the root component template using:

...>some html text content plus this is {{isActive}}<...

The shared property is passed to componentA and componentB in the html that defines them in the root component view using:

<component-a 
      is-active="isActive" 
      is-active-changed="isActiveChanged(isActive)"
   ></component-a>
   <component-b 
      is-active="isActive" 
      is-active-changed="isActiveChanged(isActive)"
   ></component-b>

The shared property is visible in componentA / componentB templates using:

...>some html text content plus this is {{$ctrl.isActive}}<...

The shared property is visible in componentA / componentB controllers using:

   this.isActive // not $scope.isActive

The shared property can be changed from componentA / componentB controllers by calling the method:

$ctrl.isActiveChanged({data: data})

Which actually will call the method in the root component controller and pass the updated value to the $scope property:

$scope.isActiveChanged(data)