[Rootpassword]

var getNextHighestZindex = function (obj){  
    var highestIndex = 0;  
   var currentIndex = 0;  
   var elArray = Array();  
    if(obj){ elArray = obj.getElementsByTagName("*"); }else{ elArray = document.getElementsByTagName("*"); }  
   for(var i=0; i < elArray.length; i++){  
      if (elArray[i].currentStyle){  
          currentIndex = parseFloat(elArray[i].currentStyle["zIndex"]);  
       }else if(window.getComputedStyle){  
          currentIndex = parseFloat(document.defaultView.getComputedStyle(elArray[i],null).getPropertyValue("z-index"));  
       }  
       if(!isNaN(currentIndex) && currentIndex > highestIndex){ highestIndex = currentIndex; }  
    }  
    return(highestIndex+1);  
}

Это максимум +1