Calculate and put value to Child table in Web Form

Hello everyone,
I’m working with web form in erpnext, I can get value and put value to field, it’s easy like work with doctype.
But now I have to meet child table, need to calculate with it, I spent a lot of time to research but still cannot find anything relate with get and put value in child table WebForm. I tried to use JavaScript to put value to Child table but not working.
Anyone have knowages about this please help. thank a lot.


I am trying to do the same thing. Did you ever find a solution to this? Thank you in advance.