var currentlayerId = "layer1";

function toglayer(id) 
{ 
if(currentlayerId) setDisplay(currentlayerId, "none"); 
if(id)setDisplay(id, "block"); 
currentlayerId = id; 
}
function setDisplay(id,value) 
{ 
var elm = document.getElementById(id); 
elm.style.display = value; 
}