Usefull for video og image backgrounds

Cover.js

/*
	
	const {x,y,width,height} = Cover (elements-width, elements-height, container-width, container-height)
	element.style.top = y + 'px'
	element.style.left = x + 'px'
	element.style.width = width + 'px'
	element.style.height = height + 'px'
	
	* Element will fill out the container like css {background-size: cover}
	* make container desired dimensions and set to overflow:hidden
	* make element "relative/absolute" and apply value
*/
export default function Cover (w, h, w2 = window.innerWidth, h2 = document.documentElement.clientHeight) {
    const ratio = h / w
    const width = (h2 / w2) > ratio ? h2 * (w / h) : w2
    const height = width * ratio
    const x = (w2 - width) * 0.5
    const y = (h2 - height) * 0.5
    return {
        x, y, width, height
    }
}