How to setup Javascript to pull one piece of information from a form

I am using a Formstack form and I’m trying to setup a counter that will show how many people have used the form. Think of it like a petition, where you have a goal number, and a counter that is going up with every submission. So, I would have some lead-in text, the counter (something like “1,576 signatures”) and then the form.

Formstack has an open API and recommended one of these options for getting this to work:

My issue is that I’m not familiar with Javascript and need help getting started.

I’ve been tasked with figuring this out so any help (even just pointing me in the right direction) would be greatly appreciated!

I’ve setup a test form/page here: