Magento – How get admin url in js file

If want to get admin URL to Magento 2 then your can try below Solution

In order to get admin URL ,you need to inject the Magento_Backend ‘s helper class Magento\Backend\Helper\Data to __construct() function.

/**
 * @var Magento\Backend\Helper\Data
 */
protected $HelperBackend;

public function __construct(
.....
\Magento\Backend\Helper\Data $HelperBackend
....
) {
$this->HelperBackend = $HelperBackend;
}

/**
 *
 * @param \Magento\Framework\Event\Observer $observer
 * @return void
 */
public function getAdminUrl()
{
echo $this->HelperBackend->getHomePageUrl();
}

define([
   'jquery',
   'mage/url'
], function ($,url) { 

  var linkUrl = url.build('frontname/regions/index');
  console.log(linkUrl);
});

Where frontname is your routes.xml file frontname.

You have to pass your frontname from routes.xml file instead of module name(namespace_module)

You can lookup your routes.xml file from app/code/Namespace/Module/etc/frontend/routes.xml