angularjs simple controller

HTML

<script src="http://ajax.googleapis.com/ajax/libs/angularjs/1.2.26/angular.min.js"></script>
<p>Try to change the names.</p>
<div ng-app="" ng-controller="personController">First Name:
    <input type="text" ng-model="firstName">
    <br>Last Name:
    <input type="text" ng-model="lastName">
    <br>
    <br>Full Name: {{firstName + " " + lastName}}</div>

JavaScript

function personController($scope) {
    $scope.firstName= "John";
    $scope.lastName= "Doe";
}