1 检测是否有选中
if(objSelect.selectedIndex > -1) {
//说明选中
} else {
//说明没有选中
}

2.动态创建select

function createSelect(){

var mySelect = document.createElement("select");    
mySelect.id = "mySelect";    
document.body.appendChild(mySelect);    
}

3.添加选项option

function addOption(){

//根据id查找对象,    
var obj=document.getElementById('mySelect');

//添加一个选项    
obj.add(new Option("文本","值"));    
}

4.删除所有选项option

function removeAll(){    
var obj=document.getElementById('mySelect');

obj.options.length=0;

}

5.删除一个选项option

function removeOne(){    
var obj=document.getElementById('mySelect');

//index,要删除选项的序号,这里取当前选中选项的序号

var index=obj.selectedIndex;    
obj.options.remove(index);    
}

6.获得选项option的值

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

var index=obj.selectedIndex; //序号,取当前选中选项的序号

var val = obj.options[index].value;

7.获得选项option的文本

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

var index=obj.selectedIndex; //序号,取当前选中选项的序号

var val = obj.options[index].text;

8.修改选项option

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

var index=obj.selectedIndex; //序号,取当前选中选项的序号

var val = obj.options[index]=new Option("新文本","新值");

9.删除select

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