建议用右键代替双击:
<script>
function show()
{ var a=document.getElementById("div1")
if (event.button==2)
{a.style.display=a.style.display=="none"?"":"none"
}
}
</script>
<select onmousedown="show()">
<option>aaaa</option>
<option>bbb</option>
<option>ccc</option>
<option>dddd</option>
</select>
<div id="div1" style="display:none">
<textarea ></textarea>
</div>
</script></head><body>
<select id="selectlist" onchange="selectvalue(this.value)">
<option value="" selected="selected">请选择值</option>
<option value="值1">值1</option>
<option value="值2">值2</option>
<option value="值3">值3</option>
<option value="值4">值4</option>
</select>
</body>