如何通过AngularJS中的指令将$invalid设置为form中的字段

<div ng-app="myApp" ng-controller="myController">
  <form name="myForm">
    <input type="text" name="myField" ng-model="myModel" required>
    <button ng-click="submitForm()">Submit</button>
  </form>
</div>

angular.module('myApp', [])
  .controller('myController', function($scope) {
    $scope.submitForm = function() {
      if ($scope.myForm.$invalid) {
        // 表单字段验证失败
        console.log('Form is invalid');
      } else {
        // 表单字段验证通过
        console.log('Form is valid');
      }
    };
  });