Browser zoom level: detecting, adjusting with Javascript

Question

In the 2-frame 'rows=' frameset I have, a user change of the zoom level to less than the 125% I coded for produces "dead space" between the frames.

In JS, is the browser's zoom level detectable, and can it be adjusted? Or have I simply forgotten a default coding consideration of some kind? (I've seen CSS's 'zoom' style, where presumably default zoom levels can be set.)

I am also seeing 'document.body.style.zoom', so seems it would be...

if (zoomLevelChange) {document.body.style.zoom= [some calculation]; }

Any help appreciated,