SO - NG Disabled not working

http://stackoverflow.com/questions/23196855/ng-disabled-in-angularjs-is-not-working-for-me

by ncapito

HTML

<link rel="stylesheet" href="http://twitter.github.com/bootstrap/assets/css/bootstrap.css">
<div ng-app>
    <div ng-controller="TodoCtrl">
        <input type="submit" value="Continue" ng-disabled="isDisabled">
        <button ng-click="inc(true)">Count up</button>
        <button ng-click="inc()">Count down</button>
    </div>
</div>

CSS

.done-true {
    text-decoration: line-through;
    color: grey;
}

JavaScript

function TodoCtrl($scope) {
    $scope.isDisabled = true;
    $scope.val = 0;
    $scope.$watch('val', function () {
        $scope.val > 3 ? $scope.isDisabled = false: $scope.isDisabled = true;
    })
    $scope.inc = function (up) {
        up ? $scope.val++ : $scope.val--;
    }
}