//1.動態創建select
function createSelect(){
var mySelect = document.createElement("select");
mySelect.id = "mySelect";
document.body.appendChild(mySelect);
}

//2.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")); //方法一：
obj.options.add(new Option("text","value")); //方法二：
for(var i=0;i<10;i++){
obj.options[i]=new Option("新文本","新值"); //方法三：
}
}

//3.刪除所有選項option
function removeAll(){
var obj=document.getElementById('mySelect');
obj.options.length=0;
}

//4.刪除一個選項option
function removeOne(){
var obj=document.getElementById('mySelect');
var index=obj.selectedIndex; //index,要刪除選項的序號
obj.options.remove(index);
}

//5.獲得選項option的值
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].value;

//6.獲得選項option的文本
var obj=document.getElementById('mySelect');
var index=obj.selectedIndex;
var val = obj.options[index].text;

//7.修改選項option
var obj=document.getElementById('mySelect');
var index=obj.selectedIndex;
var val = obj.options[index]=new Option("新文本","新值");

//8.刪除select
function removeSelect(){
var mySelect = document.getElementById("mySelect");
mySelect.parentNode.removeChild(mySelect);
}

來源：慕課網
作者：xgqfrms2015