Dynamically set a background image to a div that will keep its aspect ratio when the div resizes.

stretch.html

<div class="Item" data-stretch="images/some_image.png">

stretch.js

$('[data-stretch]').each(function(i) {
  $(this).css('background-image', 'url(' + $(this).attr('data-stretch') + ')');
});

stretch.scss

@mixin stretch-background {
  background-repeat: no-repeat;
	background-position: center center;
	background-size: cover;
}

.Item {
  @include stretch-background;
}