validation - How to access an attribute in the directive validator in AngularJS correctly -

i'm making validator validates valid dates mm/yyyy, didn't how access attribute when model changes:

<input id="my-date"        validate-short-date        data-max-date="{{thismonth}}"        type="text"        name="mydate"        data-ng-model="mymodeldate"> 

here directive

.directive('validateshortdate', ['moment', function(moment) {     return {         restrict: 'a',         require: 'ngmodel',         link: function($scope, element, attr, ngmodel) {              var maxdate = false;              var pattern, regex;             pattern = '^((0[0-9])|(1[0-2])|[1-9])\/(19|20)[0-9]{2}$';             regex = new regexp(pattern, 'i');              if(!angular.isundefined(attr.maxdate)) {                 // got once                 maxdate = attr.maxdate;             }              ngmodel.$validators.maxdate = function(modelvalue) {                 // maxdate var undefined after first time                 if (maxdate && regex.test(modelvalue)) {                     var modeldate = moment(modelvalue, 'mm/yyyy').format('yyyymm');                     return modeldate <= maxdate;                 }                 return true;             };              ngmodel.$validators.valid = function(modelvalue) {                 return modelvalue === '' || modelvalue === null || angular.isundefined(modelvalue) || regex.test(modelvalue);             };         }     }; }]) 

the validator ngmodel.$validators.valid works perfect, inside ngmodel.$validators.maxdate cannot attr.maxdate first time directive fires.

so how can access custom attribute value every time check modelvalue?

i'm not expert angularjs , i'm missing important.

the attrs argument in link function provides $observe method can use attach listener function dynamic changes in attribute value.

it simple use inside of link function:

        attr.$observe('maxdate', function() {             scope.maxdate = attr.maxdate;             ngmodel.$validate();         }); 

here working plunker