How to detect page zoom level in all modern browsers?

Question

1. How can I detect the page zoom level in all modern browsers? While this thread tells how to do it in IE7 and IE8, I can\'t find a good cross-browser solution.

Answer 1

The problem lies in the types of monitor used, a 4k monitor vs standard monitor. Chrome is by far the smartest at being able to tell us what the zoom level is just by using window.devicePixelRatio, apparently it can tell what the pixel density is and reports back the same number to matter what.

Other browsers, not so much. IE and Edge are probably the worst, as they handle zoom levels much differently. To get the same size text on a 4k monitor, you have to select 200%, instead of 100% on a standard monitor.

As of May 2018, here's what I have to detect zoom levels for a few of the most popular browsers, Chrome, Firefox, and IE11. I have it tell me what the zoom percentage is. For IE, it reports 100% even for 4k monitors that are actually at 200%, but the text size is really the same.

Here's a fiddle: https://jsfiddle.net/ae1hdogr/

If anyone would care to take a stab at other browsers and update the fiddle, then please do so. My main goal was to get these 3 browsers covered to detect if people were using a zoom factor greater than 100% to use my web application and display a notice suggesting a lessor zoom factor.