Custom Script on web form: web_form.on(field, callback) not trigger in child table

My doctype structure
field item list (child table)-> item_name, price
field total amount

expectation: In the web form, I want the total amount to update automatically whenever the item list is modified.

web_form script from example document
frappe.web_form.on: it trigger when field is updated but not working when update field is child table

I also try Client Script, It don’t work in web form, but It work only desk site

I think the solution is web form script but how to implement or which function can trigger when child table is update