var ob = document.getElementById("ifs_1"); 
if ( ob ) {
    var half = document.getElementById("ifs_1").clientWidth/2;
    var left1 = document.getElementById("ifs_1").offsetLeft;
    var left2 = document.getElementById("tmenu").offsetLeft;
    var left3 = document.getElementById("tsmenu").offsetLeft;
    var width = document.getElementById("tsmenu").clientWidth/2;
    var tsmenu = document.getElementById("tsmenu");
    tsmenu.style.left = (left1 + half + left2 - left3 - width)+"px";
}