AngularJS Example:

by jlmcdonald

HTML

<link rel="stylesheet" href="http://twitter.github.com/bootstrap/assets/css/bootstrap.css">
<div ng-app>
  <div ng-controller="MyCtrl">
    <button ng-disabled="model.questions.length > 1">button disabled by expression</button>
       <button ng-disabled="checkQuestions()">button disabled by function</button>
       <button ng-disabled="beDisabled">button disabled by bound variable</button>
  </div>
</div>

JavaScript

function MyCtrl($scope) {
    $scope.model = {questions: ["hey","ho"]};
    $scope.beDisabled=$scope.model.questions.length > 1;
    $scope.checkQuestions=function() {
        if ($scope.model.questions.length > 1) {
            return true;
        }
        else {
            return false;
        }
    }
}