When initializing a local scope property as null in Angular.js, it may end up being undefined

Recently, I created a custom Angular directive.

 <location zipcode="35423" cityname="" statecode=""></location> 

Within the directive, I defined the following:

  scope: {
                    zipcode: "@",
                    cityname: "@",
                    statecode: "@"
                },

When setting up the controller for the directive, I encountered the following:

 controller: function ($scope, $filter) {
$scope.zipcode = "35423" // assigned the value here
$scope.cityname = undefined // why is this undefined?
$scope.statecode= undefined // why is this undefined?
}

My goal is to have $scope.cityname = ""

It's worth mentioning that I am using an MVC application.

zipcode="@ZipCode" cityname="@City" statecode="@StateCode"

Additionally, in some cases, City might be null.

Answer №1

To handle undefined scope properties, you can assign them a default value of "" using the following code:

$scope.cityname = $scope.cityname || "";
.

It may seem unnecessary to do this, as both "" and undefined evaluate to false, but it can help ensure consistency in your code.

Answer №2

It appears to be a scope isolation issue that is causing the problem.

The directive is populating its scope with three values from the controller using the @ symbol in scope isolation. This means that the directive will bind these values one way, regardless of whether they are defined or not.

Since the binding is one way, changes made in the controller will be reflected in the directive, but changes made to these values in the directive will not be reflected in the controller. So, if you update a value in the directive, such as setting cityName to Islamabad, the controller will not be aware of this change and will retain the old value, which may be undefined if the variable was never initialized.

If you want two-way binding, you should use = instead of @. This will ensure that changes made to these variables in the directive will also be reflected in the controller.

For more information on scope isolation, you can refer to this article: Creating custom AngularJS directives

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