So here was my scenario:
I was creating an edit form for node type for a customer. When the node was originally submitted, the user could choose a location from a map, and the coordinates were saved in the node. And now, when a registered user is editing the node, he needs to see the map with the coordinates in place.
In order to do so, I use hook_form_alter to create a markup within the form:
$form['map_markup']['#weight'] = 16;
$form['map_markup']['#markup'] = '<div class="map-markup"><label class="control-label">Kort</label><div id="mapDiv"></div></div>';
$coords = [ 'xcoord' => $xcoord, 'ycoord' => $ycoord, ];
That's all! Now I have access to : Drupal.setting.xcoord and Drupal.setting.ycoord on the client side. Very slick!