Maybe its not too good question, but I am blank for this.

I want to make javascript file to include in client web, to call my SaaS resource, like google can call map just with this code

<script
  src="https://maps.googleapis.com/maps/api/js?key=AIzaSyB41DRUbKWJHPxaFjMAwdrzWzbVKartNGg&callback=initMap&v=weekly"
  defer
></script>

and this script can give resource like this , so the question what is keyword for make like this script and what i have to provide in my API to get it out, I know about rest api and ajax, but is it just call html from your api or what should it be?