Angular: Empty Fiddle
http://angularjs.org/
HTML
<script src="http://code.angularjs.org/angular-1.0.0rc6.js"></script>
<div ng-controller="MyCtrl">
Title: <input ng-model="title" />
<button ngDisabled="true">Update</button>
<button ng-disabled="title.trim().length>0">Validate</button>
<hr />
<button ng-click="title=''">Set title to [] (**error**)</button>
<button ng-click="title=' '">Set title to [ ]</button>
<button ng-click="title=' xx '">Set title to [ xx ]</button>
<button ng-click="title='abc'">Set title to [abc]</button>
</div>
JavaScript
var myApp = angular.module('myApp',[]);
//myApp.directive('myDirective', function() {});
//myApp.factory('myService', function() {});
function MyCtrl($scope) {
$scope.title = "";
}