I can't check for multiple choice field in angular. How can I do it?

I'm not good at Angular. I'm a trainee right now, my angular knowledge is not good. I will be grateful if you could help me. I have a multiple choice field in the front. But I am encountering an error in Js. I select one of the fields then remove it and select another field but it selects its values along with the previous selected field. So in short, I choose the value 1 at first. Then I remove that selection and select the value 2. The value comes in as "2,1". Here I normally remove the "1" value. It's coming wrong so it doesn't come.

My codes are as follows.

.cshtml:

<div style="margin:5px 0;"></div>
            <a class="btn btn-default" style="width:100%" ng-click="showFacility()">Select Store...</a>
            <div class="listbutton" ng-show="ShowFacility">
                <div class="listbox" data-offset-top="50">
                    <a class="btn btn-default allselectbutton" ng-click="checkall()">Select All</a>
                    <a class="btn btn-default allselectbutton" ng-click="checkallnot()">Remove All</a>
                </div>
                <div style="padding-top:20px;">
                    <div style="float:none;" ng-repeat="fac in facilitys">
                        <label class="checkbox-inline">
                            <input ng-model="fac.checked" type="checkbox" value="{{fac.Id}}" ng-click='Checked(fac)' /><p>{{fac.title}}</p>
                        </label>
                    </div>
                </div>
            </div>

.js:

$scope.Checkedval = "";
   $scope.CheckedId = "";
   $scope.checkall = function () {
       $scope.CheckedId = "0,4,6,7,2,5,9,8,3,10,1";
       angular.forEach($scope.facilitys, function (value, key) {
           value.checked = true;

       });
   }

$scope.checkallnot = function () {

       angular.forEach($scope.facilitys, function (value, key) {
           value.checked = false;
           $scope.CheckedId = "";
       });

   }

   $scope.Checked = function (dat) {
       $scope.a = "";
       $scope.spn = false;
       if (dat.checked) {
           $scope.spn = true;
           if ($scope.Checkedval.length == 0) {
               $scope.Checkedval = dat.title;
               $scope.CheckedId = dat.id;
           }
           else {
               $scope.Checkedval += "," + dat.title;
               if ($scope.CheckedId.length == 0) {
                   $scope.CheckedId += dat.id;
               }
               else {
                   $scope.CheckedId += "," + dat.id;
               }
           }
       } else if (!dat.checked) {

           var checkList = $scope.CheckedId.split(",");
           $scope.a += dat.id;
           var index = checkList.indexOf($scope.a);


           checkList.splice(index, 1);
           $scope.CheckedId = "";

           for (var i = 0; i < checkList.length; i++) {
               if ($scope.CheckedId.length == 0) {
                   $scope.CheckedId = checkList[i];
               } else {
                   $scope.CheckedId += "," + checkList[i];
               }
            }
       }

There is an error in my check function here. When I deselect and add another value, it comes with the previous selected value. How do I fix it so it doesn't happen? I've been trying for a while, but I couldn't. I would be glad if you help.

I can't try because I don't have full knowledge

I'm trying with Debug, I can understand where it is repeated, but unfortunately I can't change the code because my knowledge is not good.