fit image to screen properly in javascript

Question

I need to resize image from its natural size to fit the screen the same way as Chrome does with opened images in it, I wrote a rescale() function for this purpose (below).

It works mostly fine but for big landscape-oriented images (example where both width and height both exceed screen after resizing with my function http://imageontime.com/upload/big/2013/07/20/51ea60b522bba.jpg ) fullscreened image still exceeds screen by few lines at height (and rarely at width), so i wanted to ask if there is a better rescale javascript function out there or if here are any chromium source adepts who could look into chromiums source code to get the image resizing function from it so I could port it into javascript?

Here's the code:

function setautow() {
    img.style.width = 'auto';
    img.style.removeProperty("height");
    if (document.documentElement.clientHeight == 0) // Firefox again...
    {
        img.height = window.innerHeight;
    }
    else {
        img.height = document.documentElement.clientHeight;
    }
}

function setautoh() {
    img.style.height = 'auto';
    img.style.removeProperty("width");
    if (document.documentElement.clientWidth == 0) // FF
    {
        img.width = window.innerWidth;
    }
    else {
        img.width = document.documentElement.clientWidth;
    }
}

function shrink(a) {
    if (a) {
        if (img.width != document.documentElement.clientWidth) {
            setautoh();
        }
    }
    else {
        if (img.height != document.documentElement.clientHeight) {
            setautow();
        }
    }
}

var rescaled = false;

function rescale() {
    if (rescaled) {
        rescaled = false;
        img.height = img.naturalHeight;
        img.width = img.naturalWidth;
        img.style.removeProperty("height");
        img.style.removeProperty("width");
    }
    else {
        rescaled = true;
        if (img.naturalWidth > img.naturalHeight) {
            setautoh();
            setTimeout(function () {
                shrink(true);
            }, 0);
        }
        else {
            setautow();
            setTimeout(function () {
                shrink(false);
            }, 0);
        }
    }
}

Answer 1

The following seems to do the job nicely, as long as image width/height is not specified in CSS.

#Javascript
window.onresize = window.onload = function()
{
    resize();
}

function resize()
{
    var img    = document.getElementsByTagName('img')[0];
        winDim = getWinDim();


    img.style.height = winDim.y + "px";

    if (img.offsetWidth > winDim.x)
    {
        img.style.height = null;
        img.style.width = winDim.x + "px";
    }
}

function getWinDim()
{
    var body = document.documentElement || document.body;

    return {
        x: window.innerWidth  || body.clientWidth,
        y: window.innerHeight || body.clientHeight
    }
}

 

#CSS
body{
    margin:0;
    padding:0;
    text-align:center;
    background:rgb(51, 51, 51);
}

 

#HTML
<img src="http://placehold.it/4000x3000" />