获取angularjs中未定义的$scope变量

当我初始化 $scope.s 有一些价值,它工作正常。 但是,当它没有用如下所示的任何值初始化时,它会在控制台中生成错误: $scope。s未定义 单击事件绑定按钮

 var mainApp = angular.module('mainApp', ['ngRoute']);
mainApp.controller('homeCtrl', ['$scope', '$http', function ($scope, $http) {


$scope.title = 'Home page';
$scope.s = '';
$scope.m = '';
$scope.subscribe = function () {


    console.log($scope.s); // undefined


}
}]);

<div data-ng-app="mainApp" data-ng-controller="homeCtrl">
<div>
    <h1>{{title}}</h1>
</div>
<div>
    <h3>Want to become a seller and earn more..?</h3>
    <p>Add your email and we will get in touch.</p>
    <div>
        <input type="email" data-ng-model="s" id="txtEmail" />
    </div>
    <div>
        <div>                
            <button data-ng-click="subscribe();">Send</button>
        </div>            
    </div>
</div>
<div>
    {{m}}
</div>