How to use factory data in Angular?

Question

JavaScript

Greetings.
have the following code inside the controller

$scope.billings = Billing.query();

$scope.getTotalAmount = function(index){
//тут посложнее логика
            return $scope.billings[index].bills;
        }

When calling getTotalAmount() on the page, an error appears:

Can't interpolate: 
                                            {{getTotalAmount()}}
                                            
TypeError: Cannot read property 'bills' of undefined

Obviously, the data did not have time to come, but is already being requested.
I assume that promises are needed, but I can't use them.
I also tried .then and $watch, also get different errors.
send, please.

Answer 1

If you use promises, then you can do this:

$scope.getTotalAmount = function(index){
    //тут посложнее логика
    if(!$scope.billings.$resolved)
        return 0;
    return $scope.billings[index].bills;
}

But this will not help if an error occurred during the request (promise rejected).
You can do this:

$scope.getTotalAmount = function(index){
    //тут посложнее логика
    if(!$scope.billings[index])
        return 0;
    return $scope.billings[index].bills;
}

Answer 2

You have getTotalAmount function(index)
Let me explain. getTotalAmount , when called, expects you to pass it an index by which it can return $scope.billings[index].bills to you. If you do not pass index to the view by simply calling {{getTotalAmount}} instead of {{getTotalAmount(2 or any index by which you can get this is your $scope.billings[index].bills)}} you will naturally get an error, since index in your case undefined, and $scope.billings[undefined] God himself ordered to be undefined for such inputs. Well, js in general, and angular in particular, cannot guess what kind of data you expect from external approximate signs.