select多选 multiple的使用

<html>

<head>

<script type="text/javascript">

function showDiv(id){

	document.getElementById("selectOption").style.display="block";

	document.getElementById("selectOption").style.position="absolute";

	document.getElementById("selectOption").style.top=document.getElementById(id).offsetTop+25;

	document.getElementById("selectOption").style.left=document.getElementById(id).offsetLeft+20;

}

function selectM()

  {

var obj = document.getElementById("mySelect");

  alert(obj.selectedIndex);

  }

function checkselect(objname){

o = document.getElementById(objname);

t = document.getElementById("output");

var intvalue="";

for(i=0;i<o.length;i++){

   if(o.options[i].selected){

    intvalue+=o.options[i].value+",";

   }

}

t.value=intvalue.substr(0,intvalue.length-1);

alert(intvalue);

}

</script>

</head>

<body>

<form>

<div id="selectOption" style='width:100px;height:50px;z-index:100;border:1px solid #0099FF;background:#cccccc;display:none;'>

	<select id="mySelect" multiple="multiple" size="4">

	  <option value='苹果'>苹果</option>

	  <option value='桃子'>桃子</option>

	  <option value='香蕉'>香蕉</option>

	  <option value='桔子'>桔子</option>

	</select>

	<input type="button" onclick="checkselect('mySelect')" value="checkselect">

</div>

选中的项目：<input type="text" name="output">

<input id="lalla" type="button" onclick="showDiv(this.id)" value="选择">

<br/>

</form>

<p>在您点击 “选择多个” 按钮之前，请尝试同一时候选取多个选项。在点击 “选择多个” 按钮之后，请再试一次。</p>

</form>

</body>

</html>