AngularJS 'controller as' and form.$valid

Question

I want to check if a form is valid inside an angular controller. This seems straightforward when using $scope, but I can't get it to work with the 'controller as' syntax.

When I attempt to access form.$valid I get the error message "Cannot read property '$valid' of undefined".

plunkr: http://plnkr.co/edit/w54i1bZVD8UMhxB4L2JX?p=preview

HTML

<div ng-app="demoControllerAs" ng-controller="MainController as main">
  <form name="contactForm" novalidate>
    <p>
      <label>Email</label>
      <input type="email" name="email" ng-model="main.email" required />
    </p>
    <p>
      <label>Message</label>
      <textarea name="message" ng-model="main.message" required></textarea>
    </p>
    <input type="submit" value="submit" ng-click="main.submit()" />
  </form>
</div>

JS

var app = angular.module('demoControllerAs', []);

app.controller('MainController', [function () {
    var main = this;

    main.submit = function () {
        var isValid = main.contactForm.$valid;
        console.log(isValid);
    };
}]);

Answer 1

You could do as @ons-jjss suggested but if you prefer not to inject $scope into you controller, then just change your form name as

<form name="main.contactForm" novalidate>

and it'll work like a charm.

Answer 2

You need to use in this way: $scope.contactForm.$valid

EDIT

To work the above syntax, $scope needs to be inhjected in controller.

app.controller('MainController', function($scope) { 
  //code 
}