Calculating sum using Angular

Question

I'm beginner on AngularJs and I have a difficult to show the sum of two numbers. The first script work perfectly :

<div>
   <p><input type="text" ng-model="price1" /> <strong>{{price1}}</strong></p>
   <p><input type="text" ng-model="price2" /> <strong>{{price2}}</strong></p>
   <p><strong>{{total = (price1 * 1 + price2 * 1) }}</strong></p>
</div>

But when I try to test this using a controller, like this :

<div ng-controller="myCtrl">
   <p><input type="text" ng-model="price1" /> <strong>{{price1}}</strong></p>
   <p><input type="text" ng-model="price2" /> <strong>{{price2}}</strong></p>
   <p><strong>{{total}}</strong></p>
</div>
<script>
   var app = angular.module('firstApp', []);
   app.controller('myCtrl', ['$scope', function($scope) {
      $scope.total = ($scope.price1  + $scope.price2);
   }]);
</script>

I have no result, just a NaN value. I have no idea what happen !

Answer 1

There are several issues in your code:

1. The variables $scope.price1 and $scope.price2 are not defined once the controller is initialized. Arithmetical operation using undefined value produces NaN as the result.
2. You compute the $scope.total just once. Its result is not updated on change of $scope.price1 or $scope.price2
3. In the inputs you should use type="number" not type="text" then the values of $scope.price1 and $scope.price2 will be parsed and summed up as numbers. In your code they are concatenated as strings.

 var app = angular.module('myApp', []); app.controller("myCtrl", function ($scope) { $scope.price1 = 1; $scope.price2 = 2; $scope.getTotal = function() { return $scope.price1 + $scope.price2; }; }); 

 <script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script> <div ng-app="myApp"> <div ng-controller="myCtrl"> <p><input type="number" ng-model="price1" /> <strong>{{price1}}</strong></p> <p><input type="number" ng-model="price2" /> <strong>{{price2}}</strong></p> <p><strong>{{getTotal()}}</strong></p> </div> </div> 

Answer 2

Do you need to set default values? Is it saying NaN because you haven't entered anything in the input boxes?

Try initializing the variables in the controller above the total calculation.

$scope.price1 = 0;
$scope.price2 = 0;

Answer 3

The values are undefined when you call the sum, just give them an initial value

$scope.price1 = 1;
$scope.price2 = 2;
$scope.total = ($scope.price1  + $scope.price2);

What you are doing is equals to:

$scope.total = ($scope.price1  + $scope.price2);
$scope.total = (undefined  + undefined); //equals to NaN

Answer 4

I do it but I have to give a value in my controller for price1 and price2, like that :

<script>
   var app = angular.module('firstApp', []);
   app.controller('myCtrl', ['$scope', function($scope) {
      $scope.price1 = 1;
      $scope.price2 = 2;
      $scope.total = ($scope.price1 + $scope.price2);
   }]);
</script>

But I have two input. I want to use them like a calculator, put a value into them and see the result.