Javascript: I can’t find how to get the coordinates of a mouseClick relative to the ENTIRE viewable document

I need a way to find the coordinates of a mouseclick relative to the entire document. I am aware of pageX and pageY, but these values do not take in account the true entire document, or rather what I really mean is, these values do not consider the currently viewable document, AND the left over scrollable document. So while the X value is fine because this page does not scroll on the X-axis, it means that the Y value will change depending on WHERE the user is on account of the ability to scroll.

I feel like I must be missing something obvious?