Get current language of Drupal 8 in javascript?

Question

How can I get the language code or name from the Drupal javascript object in a js script ??

I know I can get language using this in php:

$language = \Drupal::languageManager()->getCurrentLanguage()->getId();

But I need to have the language in my scripts.

All i got so far is the Drupal Jquery variable

Var d = Drupal;

Which when printed looks like this.

{behaviors: {…}, locale: {…}, throwError: ƒ, attachBehaviors: ƒ, detachBehaviors: ƒ, …}
Ajax:ƒ (base, element, element_settings)
AjaxCommands:ƒ ()
AjaxError:ƒ (xmlhttp, uri, customMessage)
ProgressBar:ƒ (id, updateCallback, method, errorCallback)
Views:{parseQueryString: ƒ, parseViewArgs: ƒ, pathPortion: ƒ, getPath: ƒ}
ajax:ƒ (settings)
attachBehaviors:ƒ (context, settings)
behaviors:{autologout: {…}, drupalDisplace: {…}, responsiveImageAJAX: {…}, AJAX: {…}, activeLinks: {…}, …}
checkPlain:ƒ (str)
debounce:ƒ (func, wait, immediate)
detachBehaviors:ƒ (context, settings, trigger)
dialog:ƒ (element, options)
displace:ƒ displace(broadcast)
encodePath:ƒ (item)
formatPlural:ƒ (count, singular, plural, args, options)
formatString:ƒ (str, args)
history:{fetchTimestamps: ƒ, getLastRead: ƒ, markAsRead: ƒ, needsServerCheck: ƒ}
locale:{}
stringReplace:ƒ (str, args, keys)
t:ƒ (str, args, options)
theme:ƒ (func)
throwError:ƒ (error)
url:ƒ (path)
views:{instances: {…}, ajaxView: ƒ}
__proto__:Object

Answer 1

You can add whatever you want to the javascript via your THEMENAME.theme:

function THEMENAME_preprocess_page(array &$variables) {
    $variables['#attached']['drupalSettings']['language'] = $language;
}

After that, you can call it in javascript:

console.log(drupalSettings.language);

Edit

You need to enable drupalSettings as a dependency in your THEMENAME.libraries.yml:

frontend:
  dependencies:
    - core/drupalSettings

Answer 2

In pages with the core/drupalSettings library included, it seems to be pretty reliably available through the path:

var langCode = drupalSettings.path.currentLanguage;