How to implement dirty checking on form elements using angularjs -

i want implement dirty check on required elements in form

i have tried this

<div ng-app="">   <form name="myform" ng-controller="ctrl">     <label>         usertype:     </label>      <input name="usertype" ng-model="usertype" required>     <span class="error" ng-show="myform.usertype.$dirty">required</span><br>      <label>         designation:     </label>      <input name="designation" ng-model="designation" required>     <span class="error" ng-show="myform.designation.$dirty">required</span><br>        </form> </div>