menu [4] .onclick = function () {
dis ("menu4");
}
function dis (disp) {
 var str=document.getElementById (disp); 
 var dis=str.style.display; 
 if (dis=="none") {
 str.style.display="block"; 
} else {
 str.style.display="none"; 
}
} 
 the effect of this simple drop-down menu needs to be clicked twice to realize why and how to deal with it 
