javascript - ng-model not getting passed in has-error class -

i have template below inside directive

<input ng-model="acc" type="number" required /> <p class="input-details" ng-class="{'has-error': confirm(acc, 3, 17)}"></p> 

i have method in directive controller function

$scope.confirm= function(value, min, max) {   if (!value) return false;   return ("" + value).length < min || ("" + value).length > max; }; 

the value passed undefined in confirm method, when call same method in ng-change of input below, getting passed.

<input ng-model="acc" type="number" ng-change="confirm(acc,3,17)" required /> 

why ng-class not getting correct ng-model value?

(""+3).length = 1 || (""+17).length = 2 because of type conversion see codepen example crank number input , see (""+acc).length equals , how fix https://codepen.io/anon/pen/vkqzor

app.controller('classtesterctrl', function($scope, $log){   $scope.confirm= function(value, min, max) {     if($scope.acc < 3 || $scope.acc  > 17){       $scope.valid = false;     } else {       $scope.valid = true;     }   }; });   <div ng-app="modeltest">   <div ng-controller="classtesterctrl">     <input ng-model="acc" type="number" ng-change="confirm()" required />   <p class="input-details" ng-class="{'has-error': valid}"></p>     {{(""+acc).length}}     {{acc}}     {{valid}}   </div>   </div>