Question How can I get a javascript reference to my WebGL builds' WebAudio?

After much research I have found that WebGL builds use a HTML component to play the audio. This is not a problem at all, but I have no idea how to reference it.

I need this because I have made an audio slider that I would like to be able to control the game's main volume via the HTML Audio.

My idea is to do something like this with the reference:

Code (JavaScript):

1. document.getElementById("????").volume = _sliderValue;

I have gone through many, many posts discussing how to handle audio in js/html and I think this is how it can be done, but I just don't know how to get the reference to the WebGL player's Audio component.

If anyone knows how - or knows another way to do this - please do reply!
Thank you for taking the time to read this