<div id="follow">
<a href="#" onmouseover="showPlusMobile();" onmouseout="hidePlusMobile();" class="btn">+Follow</a>
<div class="layer_follow" id="layer_follow" onmouseover="showPlusMobile();" onmouseout="hidePlusMobile();">
<p>這是隱藏層</p>
</div>
</div>

.layer_follow
{
display:none
}

var isPlusMobileVisible=false;
var showTid;
var hideTid;
function showPlusMobile(){
if(isPlusMobileVisible == false) {
showTid = setTimeout("document.getElementById('layer_follow').style.display='block'; isPlusMobileVisible=true;", 500);
}else{
clearTimeout(hideTid);
}
}
function hidePlusMobile(){
if(isPlusMobileVisible == true) {
hideTid = setTimeout("document.getElementById('layer_follow').style.display='none'; isPlusMobileVisible=false;", 500);
}else {
clearTimeout(showTid);
}
}