javascript - angularFire 3 way data binding won't update an function -

i have firebaseobject (myfirebaseservice.getcurrentuser()) bind $scope.user. after binding successful, loop tho object see if object contain "associatedcourseid" equal value ($stateparams.id). if does, $scope.finishlessoncount count up. problem is, when add new object inside firebaseobject (that bindto user) via other page or inside firebase, finishlessoncount value won't change expect 3 way binding. need refresh page see finishlessoncount reflect true value. wrong? want finishlessoncount change using compare function add more finishedlessons firebaseobject. please see code below:

myfirebaseservice.getcurrentuser().$bindto($scope, "user").then(function(){          (var key in $scope.user.finishedlessons) {             if ($scope.user.finishedlessons.hasownproperty(key)) {                  if ($scope.user.finishedlessons[key].associatedcourseid == $stateparams.id) {                     $scope.finishlessoncount++;                 }             }         };         console.log ($scope.finishlessoncount);     }); 

update 1 according @kato solution: decide use extending firebaseoject way solute problem. still, not. did not use factory here simplify thing since need pass in courseid operation. here code:

       function countlessons(lessons, courseid) {        var count = 0;        for(var key in lessons) {           if( lessons[key].associatedcourseid ==  courseid) {              count++;           }        }        return count;     }      var userwithlessonscounter = $firebaseobject.$extend({       $$updated: function(snap) {          var changed = $firebaseobject.prototype.$$updated.call(this, snap);          this.lessoncount = countlessons(this.finishedlessons, $stateparams.id);       }     });      var reftemp = new firebase($rootscope.baseurl + "users/" + $rootscope.userid);     var usertemp = new userwithlessonscounter(reftemp);      usertemp.$bindto($scope, "usertemp").then(function(){         console.log($scope.usertemp);     });     usertemp.$watch(function() {       console.log("does run @ all? " + $scope.usertemp.lessoncount);    }); 

i update user object, lessoncount value did not change unless refresh page. , console.log inside $watch did not run @ all. wrong?

the promise returned $bindto called once. it's not event listener. can't listen updated each time there change.

please read the guide, start finish, , read angular's $watch method before continuing down route, fundamental knowledge, should not have been first instinct.

a beginner approach utilize $watch:

myfirebaseservice.getcurrentuser().$bindto($scope, "user");

$scope.$watch('user', function() {    (var key in $scope.user.finishedlessons) {       if ($scope.user.finishedlessons.hasownproperty(key)) {         if ($scope.user.finishedlessons[key].associatedcourseid == $stateparams.id) {           $scope.finishlessoncount++;         }       }    };    console.log ($scope.finishlessoncount); }); 

or, having familiarized angularfire api, 1 might pick $scope.user.$watch() in place of scope method, prove more efficient.

having written large portion of angularfire code, pick $extend tool, added precisely use cases this:

// making assumptions here since haven't included // code firebase service, not seem solid app.factory('userwithlessonscounter', function($firebaseobject) {    return $firebaseobject.$extend({       $$updated: function(snap) {          var changed = $firebaseobject.prototype.$$updated.call(this, snap);          this.lessoncount = countlessons(this.finishedlessons);          return changed;       }    }); });  function countlessons(lessons) {    var count = 0;    for(var key in lessons) {       if( lessons.hasownproperty(key) ) {          count++;       }    }    return count; } 

and in controller:

app.controller('...', function($scope, userwithlessonscounter) {    var ref = new firebase(...);    var user = new userwithlessoncounter(ref);    user.$bindto($scope, 'user');     user.$watch(function() {       console.log($scope.user.lessoncount);    }); });