Using frappe library in templates folder

Hi,
I’m trying to create dynamic pages for my website
and I’m trying to use frappe library in js files but without any success
because I need to use frappe.call and other frappe methods

for example, like this code but in my own app,


js is returning that frappe is undefined !

So is there a way to declare the frappe library in the templates folder or if not available in the public/js folder

also I tried to use jquery ajax call but the server is returning Error 500

Any Suggestions ?
Thank you all