Error on button click in Ionic framework

I am trying to learn Ionic Framework.

It might be a very simple question for the one who knows this framework. But I am not able to make this work.

What I need to do is just show alert on button click.

My index.html code contains button as:

<div class="bar bar-footer">
    <div class="title">
        <button class="button button-light" ng-click="showAlert()">
        Origin
        </button>
    </div>
</div>

This is my js code:

angular.module('todo', ['ionic'])
.controller('TodoCtrl', function($scope) {
    {
        // Use our scope for the scope of the modal to keep it simple
        scope: $scope
    }
});

$scope.showAlert = function() {
    alert("show");
};

I am getting this error on button click:

Uncaught ReferenceError: $scope is not defined app.js:9
(anonymous function)

Any idea what I am doing wrong?

please change your code 

angular.module('todo', ['ionic'])
.controller('TodoCtrl', function($scope) {
    {
        // Use our scope for the scope of the modal to keep it simple
        scope: $scope
    }
});

$scope.showAlert = function() {
    alert("show");
};

to 

angular.module('todo', ['ionic'])
.controller('TodoCtrl', function($scope) {
    {
        // Use our scope for the scope of the modal to keep it simple
            $scope.showAlert = function() {
                  alert("show");
             };
    }
});