Popup window in center screen

< script language=Javascript >
function centerPopUp( url, name, width, height, scrollbars ) {

if( scrollbars == null ) scrollbars = "0"

str = "";
str += "resizable=1,";
str += "scrollbars=" + scrollbars + ",";
str += "width=" + width + ",";
str += "height=" + height + ",";

if ( window.screen ) {
var ah = screen.availHeight - 30;
var aw = screen.availWidth - 10;

var xc = ( aw - width ) / 2;
var yc = ( ah - height ) / 2;

str += ",left=" + xc + ",screenX=" + xc;
str += ",top=" + yc + ",screenY=" + yc;
}
window.open( url, name, str );
}
< / script >

< a href="javascript:centerPopUp( 'web-design-guidelines.html', 'popup', 300, 200 )" >win open< / a >