Angular two-way data binding isolate scope directive but property is undefined?
<p>Hello I think I don't understand what two-way data binding is. First the code:</p>

<pre><code>.directive('mupStageButtons', function() {
    return {
        transclude: true,
        template: '&lt;span ng-transclude&gt;&lt;/span&gt;',
        replace: true,
        scope: {
            property: "=",
            action: "="
        },
        controller: function($scope) {
            console.log($scope); //I can see the property of $scope defined in console
            console.log($scope.property); //undefined
            this.property = $scope.property;
            this.changeStage = $scope.action; //anyway this is ok
        },
    };
})
.directive('mupStageButton', function() {
    return {
        transclude: true,
        templateUrl: '/static/templates/directives/StageButton.html',
        require: '^^mupStageButtons',
        scope: {
            value: "=",
            btnClass: "@",
        },
        link: function(scope, element, attrs, mupStageButtonsCtrl, transclude) {
            scope.property = mupStageButtonsCtrl.property;
            scope.changeStage = mupStageButtonsCtrl.changeStage;
        }
    };
})

//html

&lt;mup-stage-buttons property="company.stage" action="setStage"&gt;
    &lt;mup-stage-button value="0" btn-class="btn-default-grey"&gt;
    &lt;/mup-stage-button&gt;
&lt;/mup-stage-buttons&gt;


//controller for that html ^^^

.controller('CompanyDetailController', function($scope, $stateParams, Company){
    Company.query ({
      id : $stateParams.companyId
    }, function (data) {
      $scope.company = new Company(data);
    });
}

//template for &lt;mup-stage-button&gt;

&lt;label ng-class="property === value ? 'active' : 'btn-on-hover' " class="btn {{btnClass}}" ng-click="changeStage(value)"&gt;
    &lt;div ng-transclude&gt;&lt;/div&gt;
&lt;/label&gt;
</code></pre>

<p>Does the "=" mean, that the change in outside scope will propagate thanks to data binding? Or not? Because I fetch a $resource and it is of course defined after the time it is fetched, but the "property" remains undefined. So what is wrong?</p>

<p>EDIT: desired behavior is that the ng-class in the template for <code>&lt;mup-stage-button&gt;</code> works</p>

<p>EDIT: plunker: <a href="https://plnkr.co/edit/drXxyMpd2IOhXMWFj8LP?p=preview" rel="nofollow noreferrer">https://plnkr.co/edit/drXxyMpd2IOhXMWFj8LP?p=preview</a></p>