例子，js操作select option选中项。
<script type="text/javascript">
var selectedValue = '<%= request.getAttribute("line")%>';
function changeSelected(){
jsSelectItemByValue(document.getElementById("mySelect"),selectedValue);
}
function jsSelectItemByValue(objSelect,objItemText) {
for(var i=0;i<objSelect.options.length;i++) { //遍历select option选项
if(objSelect.options[i].value == objItemText) {
objSelect.options[i].selected = true; // option选中
break;
}
}
}
</script>
<body onload="changeSelected()">
<select id="mySelect" name="mySelect">
<option value="0">0</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
</body>