window.onresize = Setheight;
window.onload = Setheight;

function Setheight ()
{
	var viewportheight = Math.max
    (
        Math.max(document.body.scrollHeight, document.documentElement.scrollHeight),
        Math.max(document.body.offsetHeight, document.documentElement.offsetHeight),
        Math.max(document.body.clientHeight, document.documentElement.clientHeight)
    )
	document.getElementById("maincontainer").style.height = (viewportheight - 0) + 'px';
}