This is a headless polyfill for the CSS object-fit property which defines the sizing mode for content images (similar to background-size for CSS background sources).
The specification for object-fit is to be found at W3C CSS3 Images. The property scales the image to fit in a certain way into a defined area, e.g:
img {
width: 100%; // dimensions are mandatory
height: 35em; // dimensions are mandatory
object-fit: cover;
overflow: hidden; // Cuts off the parts of the image poking out
}
Normally, the image would be stretched to the specified dimensions but due to the usage of the CSS property object-fit: cover; the image now is scaled proportionally, until every pixel of the defined area is covered by parts of it. In the case of cover this means that parts of the image will overlap the given area.
The following are the possible values and their implications:
fillstreches the image exactly to the defined dimensions which results in a distorted image. Comparable tobackground-size: 100% 100%. That's the default value.noneleaves the image at its natural size and centers it inside within the defined area. If the image's natural dimensions are larger than the defined area parts of the image will poke out of it unless you also setoverflow: hiddenon it. Comparable tobackground-size: auto auto; background-position: center center.containscales the image up or down until all of it fits into the defined area. This mode respects the image's natural aspect-ratio. It's also called "letterbox view". Comparable tobackground-size: contain.coverscales the image up or down until every pixel of the defined area is covered with parts of the image. Sort of "pan and scan view". This means that parts of the image will poke out of the defined area unless you also setoverflow: hiddenon it. This mode respects the image's natural aspect-ratio. Comparable tobackground-size: cover.
The polyfill uses a feature detection method to see if object-fit is supported. If it's not it will active itself.
This polyfill works in all major browsers as well as in IE8+. Find out which browsers support object-fit natively.
- Browser | polyfill? | natively?
- Google Chrome | yes | v31+
- Opera | 14+ | (from v18 natively via experimental flag)
- Firefox | 4+ | (vote for this bug)
- Internet Explorer | 8+ |
This polyfill is available as Bower component. Use it right away from bower:
$ bower install object-fit
Or set up manually by grabbing the download from GitHub.
Then include the CSS file polyfill.object-fit.css in your HTML <head>, the JavaScript file polyfill.object-fit.min.js at the bottom of your HTML <body>. Right behind the JavaScript file reference you now need to call the polyfill:
<script>
objectFit.polyfill({
selector: 'img', // this can be any CSS selector
fittype: 'cover' // either contain, cover, fill or none
});
</script>
You can find sample implementations in our test directory.
In browsers greater IE8 the polyfill uses DOM Mutation Events or Mutation Observers (depending on what's available) to detect the injection of further images matching the defined selector. This means that it will also apply itself to any images that you append to the DOM at any later point. And it will detach itself from images that you remove from the DOM. Since this feature is sort of complicated to craft in a rock solid way, you might look out for unexpected behaviors.
This polyfill is written by Anselm Hannemann and Christian "Schepp" Schaefer. Follow them on Twitter via @helloanselm and @derSchepp or check their GitHub profiles via anselmh and Schepp for more information.
This project is under the MIT Open Source License. See the LICENSE file for more information.