registerJsVar in AssetBundle


I use assets to bundle CSS and JS for specific functions and sub-pages of my Yii2 application.
From time to time I also need to pass an Yii-generated URL (like Url::toRoute([‘ajax/get’]) ) to Js-side using registerJsVar - method.

I’m not sure, where the best place for \Yii::$app->clientScript->registerJsVar is, so i decided to put this in the init() section of the related AssetBundle. Now CSS & JS files & JS parameters (like this url) er bundled in one place: the AssetBundle.
My init() method of the bundle looks like that:

    public function init()
        $ajaxGetUrl = Url::toRoute(['ajax/get']);
        \Yii::$app->clientScript->registerJsVar ('g_ajaxGetUrl', $ajaxGetUrl, \Yii::$app->clientScript::POS_HEAD);

But this will not work and I get the following error: " Getting unknown property: yii\web\Application::clientScript"
Any ideas how to fix this?
Is this the wrong place for registering JS vars?

Thank you.