How to use 'this' in javascript in repeater

I have a repeater that contains a form.
I want to disable the button if the form is submitted in the repeater.

I’ve tried a number of things but nothing is working.

• Tried passing this into a javascript function - apparently it gets a handle to the flowcontrol object
• Tried passing $index into it and it’s not running my function at all:
  dmx-on:click=“run({runJS:{function:‘disable_btn’,args:[’{{$index}}’]}})”
• Tried creating an onsubmit event on the form passing in the index - the onsubmit event isn’t rendered in the HTML

any other suggestions?