//動態創建select
function createSelect()
{
var mySelect = document.createElement("select");
mySelect.id = "mySelect";
document.body.appendChild(mySelect);
}

//添加選項option
function addOption()
{
//根據id查找對象，
var obj=document.getElementById('mySelect');
//添加一個選項
obj.add(new Option("文本","值")); //這個只能在IE中有效
obj.options.add(new Option("text","value")); //這個兼容IE與firefox
}

//刪除所有選項option
function removeAll()
{
var obj=document.getElementById('mySelect');
obj.options.length=0;
}

//刪除一個選項option
function removeOne()
{
var obj=document.getElementById('mySelect');
//index,要刪除選項的序號，這里取當前選中選項的序號
var index=obj.selectedIndex;
obj.options.remove(index);
}

//獲得選項option的文本
var obj=document.getElementById('mySelect');
var index=obj.selectedIndex; //序號，取當前選中選項的序號
var val = obj.options[index].text;

//修改選項option
var obj=document.getElementById('mySelect');
var index=obj.selectedIndex; //序號，取當前選中選項的序號
var val = obj.options[index]=new Option("新文本","新值");