<button id="button ">rkbr</button>
<select id="select ">
<option>eee</option>
<option>eee</option>
<option>eee</option>
<option>eee</option>
<option>eee</option>
<option>eee</option>
<option>eee</option>
<option>eee</option>
</select>
$("#button").on("click",function(){
var sl=$("#select");
sl.show();
sl[0].size=2;
});
$("#select").on("click",function(){
var sl=$(this);
sl.hide();
});
$(function() {
$("#button").on("click",function(){
var s = $("#select").attr('size')==1?8:1;
$("#select").attr('size', s);
});
});