Customer and Company Data displaying via Javascript (NO PHP)

I’ve tried researching this like crazy, and all I’ve come up with is PHP solutions.. which sadly, our Magento 2 site is managed by Magento Certified third-party, and I don’t have access to play around with the themes or PHP files myself..

(and yes, I know that is technically the ‘better way’ of doing things.. but obviously some values are already accessible without doing so, and that’s what I’m looking for.. just whatever is already accessible without making file changes.)

I’m simply trying to find a list of variables (? not really sure what to call these, specifically.) that I can pull with just HTML or Javascript, to use in Magento’s built in CMS Blocks, dynamic pages, etc.; such as the following example..

I know that I can use something like this to pull the Customer’s First Name (also ‘fullname’ works, but I don’t know what else does.):

<div data-bind="scope: 'customer'" style="display: none;">
    <span data-bind="text: customer().firstname">
</div>

Is there a list somewhere of other attribute-names I can use to get other values? Also, what are some of the other scopes, and some of their values? (Company, etc.?)

Thanks in advance!

EDIT: Furthermore, could someone please demonstrate how to write the code I showed above but just in Javascript, so I’m not actually creating a hidden DOM element, just to get the value from? (Currently I’m using JS to find that element by ID, and storing it’s contents into a variable of its own, which is obviously not very efficient at all.)