Custom triggers

Hey,
I’m trying to notify the user of something based on a custom field in the item doctype when the user selects an item in a sales order.
I cannot find the necessary trigger to react after the user finished selecting the item (when he clicks on “done”)

script is client-side (js).

any help would be appreciated.

Whats your use-case, easiest to do it on save using Email Alerts

https://manual.erpnext.com/contents/setting-up/email/email-alerts