Directive Angularjs : Confirm password

match-password-directive.js

angular.module('app')
  .directive('validateEquals', function () {
    return {
      require: 'ngModel',
      link: function(scope, element, attrs, ngModelCtrl) {
        function validateEqual(value) {
          var valid = (value === scope.$eval(attrs.validateEquals));
          ngModelCtrl.$setValidity('equal', valid);
          return valid ? value: 'undefined';
        }
        ngModelCtrl.$parsers.push(validateEqual);
        ngModelCtrl.$formatters.push(validateEqual);
        scope.$watch(attrs.validateEquals, function() {
          ngModelCtrl.$setViewValue(ngModelCtrl.$viewValue);
        })
      }
    };
  });

view.html

<form ng-submit="submit()" name="register" novalidate>
  <h2 class="text-center">Register</h2>
  <div class="form-group">
    <label for="exampleInputEmail1">Email address</label>
    <input name="email" ng-model="email" type="email" class="form-control" id="exampleInputEmail1" placeholder="Email" required>
    <p class="help-block" ng-show="register.email.$dirty && register.email.$invalid">Please enter a proper email.</p>
  </div>
  <div class="form-group">
    <label for="passwordInput">Password</label>
    <input name="password" ng-model="password" type="password" class="form-control" id="passwordInput" placeholder="Password" required>
  </div>
  <div class="form-group">
    <label for="confirmPasswordInput">Confirm Password</label>
    <input name="password_confirm" ng-model="password_confirm" type="password" class="form-control" id="confirmPasswordInput" placeholder="Confirm Password" validate-equals="password">
  </div>
  <p class="help-block" ng-show="register.password_confirm.$dirty && register.password_confirm.$invalid ">Please match the Passwords</p>
  <div class="text-center">
    <button type="submit" class="btn btn-primary btn-lg" ng-disabled="register.$invalid">Submit</button>
  </div>
</form>