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