window.onload = function() {    
    if (document.getElementById('theLayer')) {
        var w = 0;
        var h = 0;
        //IE
        if (!window.innerWidth) {
            //strict mode
            if (!(document.documentElement.clientWidth == 0)) {
                w = document.documentElement.clientWidth;
                h = document.documentElement.clientHeight;
            }
            //quirks mode
            else {
                w = document.body.clientWidth;
                h = document.body.clientHeight;
            }
        }
        //w3c
        else {
            w = window.innerWidth;
            h = window.innerHeight;
        }
        var browserbreedte = Math.floor(w);
        var layerbreedte = Math.floor(document.getElementById('theLayer').style.width.replace('px', ''));
        var positielinks = Math.floor((browserbreedte / 2) - (layerbreedte / 2));
        document.getElementById('theLayer').style.left = positielinks-50 + 'px';
        document.getElementById('theLayer').style.visibility = 'visible';
    }
}
function layer_sluiten(){
	document.getElementById('theLayer').style.visibility = 'hidden';
}