function getDocHeight() {
    var D = document;
    return Math.max(
        Math.max(D.body.scrollHeight, D.documentElement.scrollHeight),
        Math.max(D.body.offsetHeight, D.documentElement.offsetHeight),
        Math.max(D.body.clientHeight, D.documentElement.clientHeight)
    );
}	
function getDocWidth() {
    var D = document;
    return Math.max(
        Math.max(D.body.scrollWidth, D.documentElement.scrollWidth),
        Math.max(D.body.offsetWidth, D.documentElement.offsetWidth),
        Math.max(D.body.clientWidth, D.documentElement.clientWidth)
    );
}	

document.getElementById('preloader').style.height = getDocHeight()+'px'
document.getElementById('preloader').style.width = getDocWidth()+'px'