[Андрей Параничев]

SunYang,
Попробуйте так:

function on_panel() {
     if(lem.style.visibility=="hidden") {
          on_id = event.srcElement
          num_id = on_id.id;
          lem=document.getElementById("u_"+num_id);
          coord=window.event;
          lem.style.top=coord.clientY+20;
          lem.style.left=coord.clientX+20;
          lem.style.visibility="visible";
          xinterval = setInterval("wrtext()", 50)
     } else {
          lem.style.visibility="hidden";
          lem.innerHTML = "";
          i = 0; 
     }
}