AngularJS directive with asynchronous parameters in scope

Question

I am trying to make a directive for an easier access to the static datas in my app. In my $rootScope, I have a params object which contains static datas coming from the backend server. The goal of this directive is to access to the params object easy in the html code. There are 2 parameters :

param-name which contains the name of the requested object
param-id which contain the key of the object to access

The result is the title attribute of the request object.

In my HTML code, I have

<ng-params param-name="ContactOrigins" param-id="contact.origin_id"></ng-params>

In my JS code, I have :

myApp.directive('ngParams',
    function($rootScope){
        return{
            restrict: 'E',
            template : '<span>{{value}}</span>',
            scope: {
                paramName: '@',
                paramId: '='
            },
            link: function(scope,element,attrs){
                var tab = $rootScope.params[scope.paramName];
                console.log(scope.paramId);
                scope.value = '';
                for(var i = 0; i < tab.length; i++) {
                    if(tab[i]['id'] == scope.paramId) {
                        scope.value = tab[i]['title'];
                    }
                };
                if(scope.value == '')
                    scope.value = '<em>Not specified</em>'
            }
        }
    }
);

When the page is loaded, the console.log(scope.paramId) give me an "undefined" result. So it doesn't work properly. The thing is that the object contact is loaded asynchronously through an $http request to the backend server. And my idea is that the $http request is not yet resolved and the directive tries to operate with an empty object. A last additional point : The directive works perfectly when I put an hard coded value in the param-id attribute (param-id="3" for example).

My first question is : Am I right with my idea ? My second question is : Is there any way to workaround this problem ? Is it possible to postpone the directive compilation until the $http is resolved ?

You should watch the paramId for changes. See stackoverflow.com/questions/15112584/… — crackmigg
– crackmigg, Commented Feb 18, 2016 at 17:33
That's a good idea but it seems that we are missing something. I added the `scope.$watch('paramId', function(){ console.log(scope.paramId); });' in my link function but it is still "undefined"... — user2126372
– user2126372, Commented Feb 18, 2016 at 17:44
It will be undefined on the first run, but change when $http is resolved as you are saying in your description. The watch will execute again. — crackmigg
– crackmigg, Commented Feb 18, 2016 at 17:51
Sorry, I talked too fast... You are right and it works perfectly i Many thanks @migg — user2126372
– user2126372, Commented Feb 18, 2016 at 18:00

user2126372 · Accepted Answer · 2016-02-18 18:03:10Z

As @migg told me, the solution is to use $watch...

timmApp.directive('ngParams',
    function($rootScope){
        return{
            restrict: 'E',
            templateUrl : 'js/directives/_params.html',
            scope: {
                paramName: '@',
                paramId: '='
            },
            link: function(scope,element,attrs){
                scope.value = '';
                scope.$watch('paramId', function(){
                    if(typeof scope.paramId != 'undefined'){
                        var tab = $rootScope.params[scope.paramName];
                        for(var i = 0; i < tab.length; i++) {
                            if(tab[i]['id'] == scope.paramId) {
                                scope.value = tab[i]['title'];
                            }
                        };
                    }
                });
            }
        }
    }
);

Thank you @migg !!!

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