Email id in billing address for particular customer in sales invoice or sales order

I want to send sales invoice pdf to customer So when I clicked on email there should be recipients email id by default which is as a email -id for that customer in its billing address.
for this I try to overrides …/apps/frappe/frappe/public/js/frappe/views/communication.js for my app but it does not work .I also modify
app_include_js = “/assets/techseria/js/frappe/views/communication.js”
it shows error on the first line which is
import localforage from “localforage”;
please guide me as I am new to frappe/ERPNext
or suggest any better way to do my task
Thanks in advance