Resize div with aspect ratio to fit content css image

Question

Hello I have a div and as background I have an image with width 1920px and height 1200px. divs have 100% width and window.innerHeight on document ready;

The background css images have the follwoing rule: background-size: 100% auto !important; so that they are responsive

What I would like to do is based on window.resize calculate the new height for the div element and set it so that it matches the background-images css height.

Answer 1

newHeight = (1200 * divWidth) / 1920

Answer 2

If I understand you right you don't need js

background: url(../img/image.png) no-repeat center top fixed; 
-webkit-background-size: cover;
-moz-background-size: cover;
-o-background-size: cover;
background-size: cover;