you plunk link is not working. I don't know what exactly happen in your code.
I think maybe your miss ng-model, ng-model is the way to do two-way data binding in angular .
for example
<input type="text" datepicker-popup="dd-MMMM-yyyy" ng-model="dt" />
in this example date is binding to dt (ng-model="dt")
you can get data by $scope.dt if you want to watch the date change you can do
$scope.$watch('dt',function(val){
//to do
console.log(val)
})