Adding Custom JS Code in Validation Rule using VBS

Summary:

Our requirement is to validate the National ID field available on the "Hire an employee" Page, using an External Webservice which we want to invoke on click of the Save Button or when the National ID input is being changed. While exploring "Validation" feature we saw the functionality to add custom JS code in it as well, which we wanted to understand whether we can use to invoke external APIs or Oracle APIs, so needed a few clarifications.

1. Can we add event listeners like "click" or "onchange" on the elements like Save Button/National ID Textfield.
2. How do we get the identifiers for these elements?