check passwords with angularjs's directive

directive.js

.directive('equals', function() {
  return {
    restrict: 'A', // only activate on element attribute
    require: '?ngModel', // get a hold of NgModelController
    link: function(scope, elem, attrs, ngModel) {
      if(!ngModel) return; // do nothing if no ng-model
 
      // watch own value and re-validate on change
      scope.$watch(attrs.ngModel, function() {
        validate();
      });
 
      // observe the other value and re-validate on change
      attrs.$observe('equals', function (val) {
        validate();
      });
 
      var validate = function() {
        // values
        var val1 = ngModel.$viewValue;
        var val2 = attrs.equals;
 
        // set validity
        ngModel.$setValidity('equals', val1 === val2);
      };
    }
  }
});

inputs.html

<input ng-model="user.password" />
<input ng-model="user.confirmation" equals="{{ user.password }}" />