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

In Internet Explorer 7, 8 & 9, this works:

function getZoom() {
    var screen;

    screen = document.frames.screen;
    return ((screen.deviceXDPI / screen.systemXDPI) * 100 + 0.9).toFixed();
}

The "+0.9" is added to prevent rounding errors (otherwise, you would get 104% and 109% when the browser zoom is set to 105% and 110% respectively).

In IE6 zoom doesn't exists, so it is unnecessary to check the zoom.