Custom Validation in AngularJS

 Custom validations in Angular JS are created as directives with a dependency on the ng-model directive. 
 
 app.directive('evenNumber', function() {
      return {
        require: 'ngModel',
        link: function(scope, element, attr, ctrl) {
          function isEven(value) {
            if (parseInt(value, 10) % 2 === 0) {
              ctrl.$setValidity('even', true);
            } else {
              ctrl.$setValidity('even', false);
            }
              return value;
          }
          ctrl.$parsers.push(isEven); // Do not forget this
        }
      };
  });
  
  Remember, when naming a directive, you must use a camel case name(like evenNumber) but 
  when invoking it, you must use - separated name (like even-number).