Moodle in English

I need to call a webservice from within the mobile.js code of an assignment submission plugin I'm trying to enable for the mobile app. I've had a look here: https://docs.moodle.org/dev/Mobile_support_for_plugins But the examples all seem to relate to tying a button in the template to a webservice to send data to that webservice, which isn't what I need to do. Can somebody point me at an example of how to do this? I'm struggling to find anything that helps.