//1.动态创建selectfunction createSelect(){    var mySelect = document.createElement("select");    mySelect.id = "mySelect";     document.body.appendChild(mySelect);}//2.添加选项optionfunction 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"));    //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.删除所有选项optionfunction removeAll(){    var obj=document.getElementById(‘mySelect‘);    obj.options.length=0;}//4.删除一个选项optionfunction removeOne(){    var obj=document.getElementById(‘mySelect‘);    var index=obj.selectedIndex;    //index,要删除选项的序号    obj.options.remove(index);}//5.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;//6.获得选项option的文本var obj=document.getElementById(‘mySelect‘);var index=obj.selectedIndex;    var val = obj.options[index].text;//7.修改选项optionvar obj=document.getElementById(‘mySelect‘);var index=obj.selectedIndex;    var val = obj.options[index]=new Option("新文本","新值");//8.删除selectfunction removeSelect(){    var mySelect = document.getElementById("mySelect");    mySelect.parentNode.removeChild(mySelect);}