AngularJS Tutorial #25: How to Use Constants

In this tutorial, we will be discussing how to use constants in AngularJS. Constants are used to define values that remain constant throughout the application’s lifecycle. They are useful for storing values such as API endpoints, configuration settings, or any other value that should not be changed during the application’s runtime.

To define a constant in AngularJS, you can use the constant method provided by the angular.module function. Constants can be injected into controllers, services, and other components in the same way as services and factories.

Here’s an example of how to define a constant in AngularJS:

angular.module('myApp').constant('API_URL', 'https://api.example.com');

In this example, we define a constant named API_URL with the value 'https://api.example.com'. Now, let’s see how we can use this constant in our application.

1. Inject the constant into a controller or service:

angular.module('myApp').controller('MyController', function(API_URL) {
  console.log('API URL:', API_URL);
});

In this controller, we inject the API_URL constant and log its value to the console.

1. Use the constant in a template:

<div ng-controller="MyController">
  <p>API URL: {{ API_URL }}</p>
</div>

In this template, we use the API_URL constant to display its value in the HTML.

1. Define multiple constants:

You can define multiple constants in the same way as shown above. For example:

angular.module('myApp').constant('APP_NAME', 'My Awesome App');
angular.module('myApp').constant('LOCALE', 'en_US');

1. Using constants in config blocks:

Constants can also be injected into config blocks to configure services or set up the application. Here’s an example:

angular.module('myApp').config(function(API_URL, $httpProvider) {
  $httpProvider.defaults.headers.common['Authorization'] = `Bearer ${API_URL}`;
});

In this config block, we inject the API_URL constant and set the default authorization header for all HTTP requests.

Overall, constants in AngularJS are a useful tool for defining values that should not change throughout the application’s lifecycle. They can be injected into various components and used to configure different aspects of the application. I hope this tutorial has been helpful in understanding how to use constants in AngularJS. Thank you for reading!