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);????
}