正确缩放图像但适合div内部

Question

I am making an image gallery. This is the HTML for the image:

<div style="width: 84%; height: 100%; float: left; text-align: center;"><img
id="mainimage" style="height: 100%;" 
src="http://www.gymheroapp.com/workouts/img/spinner.gif"/></div>
<!-- Loading spinner is temp image, will be replaced by Javascript later -->

It works fine when the image is square, or the width is not too much more than the height. It breaks when the width is too great, though. Example of image overflowing:

Is there a way I could check whether there is overflow within my Javascript? Something like this:

image.setAttribute('height', '100%')
image.removeAttribute('width')
if (image.isOverflowing()) {
    image.setAttribute('width', '100%')
    image.removeAttribute('height')
}

Even better, is there any way to scale the image properly but fit it withing the containing div ?

Answer 1

jquery example

Best fit:

$('img').on('load',function(){
    var css;
    var ratio=$(this).width() / $(this).height();
    var pratio=$(this).parent().width() / $(this).parent().height();
    if (ratio<pratio) css={width:'auto', height:'100%'};
    else css={width:'100%', height:'auto'};
    $(this).css(css);
});

Edit to account for caveat where image is in cache

$('img').on('bestfit',function(){
    var css;
    var ratio=$(this).width() / $(this).height();
    var pratio=$(this).parent().width() / $(this).parent().height();
    if (ratio<pratio) css={width:'auto', height:'100%'};
    else css={width:'100%', height:'auto'};
    $(this).css(css);
}).on('load', function(){
    $(this).trigger('bestfit');
}).trigger('bestfit');

Answer 2

Heres a simple CSS solution:

html, body { height: 100%; }
#gallery { height: 100%; width: 100%; position: relative; }

#gallery img {
  /* CSS Hack will make it width 100% and height 100% */
  position: absolute;
  top: 0px;
  right: 0px;
  bottom: 0px;
  left: 0px;
  /* Maintain aspect ratio */
  max-height: 100%;
  max-width: 100%;
}

<div id="gallery">
  <img src="http://cl.vvmonnickendam.nl/files/large/87" alt="Awesome blabla gedoe">
</div>

Fiddle example