Zoom Body Browser

Zoom body browser

zoom is a non-standard property that has not been implemented by Firefox, the closest cross-browser property is transform (demo):

document.body.style.transform = 'scale(2)';

The effect, however, will be different from applying zoom: parent context (e.g. width, height) will not be updated. If that's your intent, you may want to consider using calc() and a multiplier on selected properties:

document.body.style['--zoom'] = '2';
document.body.style.fontSize = 'calc(16px * var(--zoom))`;

How to detect page zoom level in all modern browsers?

Now it's an even bigger mess than it was when this question was first asked. From reading all the responses and blog posts I could find, here's a summary. I also set up this page to test all these methods of measuring the zoom level. [↑ broken link. Archived copy → here].

Edit (2011-12-12): I've added a project that can be cloned: https://github.com/tombigel/detect-zoom

• IE8: screen.deviceXDPI / screen.logicalXDPI (or, for the zoom level relative to default zoom, screen.systemXDPI / screen.logicalXDPI)
• IE7: var body = document.body,r = body.getBoundingClientRect(); return (r.left-r.right)/body.offsetWidth; (thanks to this example or this answer)
• FF3.5 ONLY: screen.width / media query screen width (see below) (takes advantage of the fact that screen.width uses device pixels but MQ width uses CSS pixels--thanks to Quirksmode widths)
• FF3.6: no known method
• FF4+: media queries binary search (see below)
• WebKit: https://www.chromestatus.com/feature/5737866978131968 (thanks to Teo in the comments)
• WebKit: measure the preferred size of a div with -webkit-text-size-adjust:none.
• WebKit: (broken since r72591) document.width / jQuery(document).width() (thanks to Dirk van Oosterbosch above). To get ratio in terms of device pixels (instead of relative to default zoom), multiply by window.devicePixelRatio.
• Old WebKit? (unverified): parseInt(getComputedStyle(document.documentElement,null).width) / document.documentElement.clientWidth (from this answer)
• Opera: document.documentElement.offsetWidth / width of a position:fixed; width:100% div. from here (Quirksmode's widths table says it's a bug; innerWidth should be CSS px). We use the position:fixed element to get the width of the viewport including the space where the scrollbars are; document.documentElement.clientWidth excludes this width. This is broken since sometime in 2011; I know no way to get the zoom level in Opera anymore.
• Other: Flash solution from Sebastian
• Unreliable: listen to mouse events and measure change in screenX / change in clientX

Here's a binary search for Firefox 4, since I don't know of any variable where it is exposed:

<style id=binarysearch></style>
<div id=dummyElement>Dummy element to test media queries.</div>
<script>
var mediaQueryMatches = function(property, r) {
  var style = document.getElementById('binarysearch');
  var dummyElement = document.getElementById('dummyElement');
  style.sheet.insertRule('@media (' + property + ':' + r +
                         ') {#dummyElement ' +
                         '{text-decoration: underline} }', 0);
  var matched = getComputedStyle(dummyElement, null).textDecoration
      == 'underline';
  style.sheet.deleteRule(0);
  return matched;
};
var mediaQueryBinarySearch = function(
    property, unit, a, b, maxIter, epsilon) {
  var mid = (a + b)/2;
  if (maxIter == 0 || b - a < epsilon) return mid;
  if (mediaQueryMatches(property, mid + unit)) {
    return mediaQueryBinarySearch(
        property, unit, mid, b, maxIter-1, epsilon);
  } else {
    return mediaQueryBinarySearch(
        property, unit, a, mid, maxIter-1, epsilon);
  }
};
var mozDevicePixelRatio = mediaQueryBinarySearch(
    'min--moz-device-pixel-ratio', '', a, b, maxIter, epsilon);
var ff35DevicePixelRatio = screen.width / mediaQueryBinarySearch(
    'min-device-width', 'px', 0, 6000, 25, .0001);
</script>

How can I 'page zoom' on mobile browser

Apologies for answering my own question, but after a lot of tinkering, I found a way that works for me and seems to work on most web sites, so I thought it was worth sharing:

function zoom(scale) {
    document.body.style.transform = "scale(" + scale + ")";
    document.body.style.transformOrigin = "top left";
    document.body.style.width = (100 / scale) + "%";
    document.body.style.height = (100 / scale) + "%";
};
zoom(1.25);

The trick is to scale up the body with a scale transform, but then reduce the height and width. Reducing the height and width causes it to re-flow and keep the transformed content on the screen.

I tested the above code by pasting it into the console of Chrome Firefox and IE on several popular websites. It seems to perfectly re-scale amazon.com and stackoverflow.com, but not gmail. My own web app needed the patches described below.

Fuller solution with patches for jQuery:

With the above solution (and after pinch zoom), issues occur when JavaScript tries to measure pixel positions and use them to position other elements. This is because functions like getBoundingClientRect() returns coordinates multiplied by scale. If you use jQuery .height(), .width(), offset() etc. you get the same issue; all jQuery docs says, "dimensions may be incorrect when the page is zoomed by the user".

You can fix jQuery methods like .width() so deliver values as they would be if were viewing it with scale = 1.

Edit since jQuery 3.2.0: height(), width(), etc. have been fixed and do not require the patch shown below. But offset() still needs the patch and if you use $(window).height() or width() to find the size of the view-port you will need to divide by scale.

var zoom = (function () {
    var scale = 1, recurLev = 0;
    function alter(fn, adj) {
        var original = $.fn[fn];
        $.fn[fn] = function () {
            var result;
            recurLev += 1;
            try {
                result = original.apply(this, arguments);
            } finally {
                recurLev -= 1;
            }
            if (arguments.length === 0 && recurLev === 0) {
                result = adj(result);
            }
            return result;
        };
    }
    function scalePos(n) { return n / scale; }
    /* Not needed since jQuery 3.2.0
    alter("width", scalePos);
    alter("height", scalePos);
    alter("outerWidth", scalePos);
    alter("outerHeight", scalePos);
    alter("innerWidth", scalePos);
    alter("innerHeight", scalePos);
    */
    alter("offset", function (o) { o.top /= scale; o.left /= scale; return o; });
    return function (s) {
        scale = s;
        document.body.style.transform = "scale(" + scale + ")";
        document.body.style.transformOrigin = "top left";
        document.body.style.width = (100 / scale) + "%";
        document.body.style.height = (100 / scale) + "%";
    };
}());
zoom(1.25);

The only other issue I found was in code (like dragging and drawing etc) that uses positions from events like mousedown, touchstart, mousemove, touchmove etc. I found you had to scale pageX and pageY by dividing them by scale.

When I zoom in the browser, the document.body.clientWidth changed

Isn't it 1000/150*100?
The size of browser window (the browser viewport, NOT including toolbars and scrollbars).

ClientWith only works in IE5-8 by the way. You could you use window.innerWidth for other modern browsers and above IE8

zoom an application to 80% by css

This is really not possible with CSS and/or JQuery.
Manual browser zoom and CSS zoom property both work differently and will produce different results.

source:
Changing the browser zoom level

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Alternative: On page load provide users with a modal window instructing them how to manually Zoom in/out, close it after they have zoomed successfully.

How to set zoom levels in chrome browser using watir webdriver(ruby watir- set specific zoom level / zoom out /zoom in)

It's common notion that when people use selenium,they tend to use driver variable, but when people use WATIR they use browser, so use browser instead of driver.

And to answer your question, you can use the following code to set up your zoom level.

browser=Watir::Browser.new :chrome
browser.execute_script("document.body.style.zoom='75%'")

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