How do I get my directive to only fire on onchange?

Question

I've defined a directive like so:

angular.module('MyModule', [])
    .directive('datePicker', function($filter) {
        return {
            require: 'ngModel',
            link: function(scope, elem, attrs, ctrl) {
                ctrl.$formatters.unshift(function(modelValue) {
                    console.log('formatting',modelValue,scope,elem,attrs,ctrl);
                    return $filter('date')(modelValue, 'MM/dd/yyyy');
                });
                ctrl.$parsers.unshift(function(viewValue) {
                    console.log('parsing',viewValue);
                    var date = new Date(viewValue);
                    return isNaN(date) ? '' : date;
                });
            }
        }
    });

The parser seems to fire every time I type a key in my textbox though -- what exactly is the default event, is it keyup, or input? And how do I change it to only fire onchange? It really isn't necessary to fire anymore often than that.

Furthermore, I'm actually manipulating the content of this input using jQuery UI's datepicker. When clicking on the calendar it doesn't seem to trigger the appropriate event that causes the model to be updated/parser to be triggered. I think I can force an event to be fired but I need to know which one.

---

Trying to use scope.$apply() but that doesn't seem to help any:

.directive('datepicker', function($filter) {
    return {
        require: 'ngModel',
        link: function(scope, elem, attrs, ctrl) {
            $(elem).datepicker({
                onSelect: function(dateText, inst) {
                    console.log(dateText, inst);
                    scope.$apply();
                }
            });
            ctrl.$formatters.unshift(function(modelValue) {
                console.log('formatting',modelValue);
                return $filter('date')(modelValue, attrs.datePicker || 'MM/dd/yyyy');
            });
            ctrl.$parsers.unshift(function(viewValue) {
                console.log('parsing',viewValue);
                return new Date(viewValue);
            });
        }
    }
})

---

I don't think the solution given here works for me because (a) I want to use the datepicker attribute value for choosing a date format or other options, but more importantly, (b) it seems to be passing back a string to the model when I want an actual date object... so some form of parsing has to be done and applied to the ng-model.

Answer 1

Here I created a mo-change-proxy directive, It works with ng-model and it updates proxy variable only on change.

In this demo I have even included improved directive for date-input. Have a look.
Demo: http://plnkr.co/edit/DBs4jX9alyCZXt3LaLnF?p=preview

angModule.directive('moChangeProxy', function ($parse) {
    return {
        require:'^ngModel',
        restrict:'A',
        link:function (scope, elm, attrs, ctrl) {
            var proxyExp = attrs.moChangeProxy;
            var modelExp = attrs.ngModel;
            scope.$watch(proxyExp, function (nVal) {
                if (nVal != ctrl.$modelValue)
                    $parse(modelExp).assign(scope, nVal);
            });
            elm.bind('blur', function () {
                var proxyVal = scope.$eval(proxyExp);
                if(ctrl.$modelValue != proxyVal) {
                    scope.$apply(function(){
                        $parse(proxyExp).assign(scope, ctrl.$modelValue);
                    });
                }
            });
        }
    };
});