title: Angularjs get form field validity inside directive
body: <p>I'm hoping this isn't a duplicate - plenty of similar questions about but I can't find an answer that works. </p>
  
  <p>I have an Angular directive, thus:</p>
  
  <pre><code>app.directive('emailInput', function(){
      return {
          restrict: 'E',
          templateUrl: 'template.html',
          link: function(scope, elem, attrs, ctrl){
              elem.bind('keyup', function(){
                  // TODO - what?
              })
          }
      }
  }
  </code></pre>
  
  <p>and in the template html: </p>
  
  <pre><code>&lt;input type="email" required ng-model="emailAddress" /&gt;
  </code></pre>
  
  <p>Without knowing the name of the form, inside the <code>link</code> function, I want to know the value of the <code>emailAddress.$valid</code> property - how can I get this?</p>