Why is my Angular Controller Undefined, and How Do I Fix It?

Defining Controllers Globally in Angular: Error and Solutions

Error Encountered:
Angular applications occasionally encounter an error indicating that a controller is not recognized as a function, resulting in an undefined status. This error can surface during controller definition at the global level.

Solution:
Starting with Angular 1.3, global controller declaration is deprecated. Controllers must now be registered using the 'module.controller' syntax.

Traditional Method (Deprecated):

function ContactController($scope) {
  // Controller logic
}

Revised Method (Angular 1.3 ):

Option 1:

// Register the controller
angular.module('app').controller('ContactController', ['$scope', function ContactController($scope) {
  // Controller logic
}]);

Option 2:

// Define the controller as a function
function ContactController($scope) {
  // Controller logic
}
// Register the controller with its dependency injection
ContactController.$inject = ['$scope'];
angular.module('app').controller('ContactController', ContactController);

Additional Considerations:

• Ensure that you have specified the app name in the ng-app directive on the root HTML element (e.g., ng-app="myApp").
• Verify that the correct scripts are included in the application.
• Avoid defining the same module more than once, as it can overwrite previously registered controllers and cause the error.

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