1. The dynamic creation of select 
 function createSelect(){

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

2. Add Options 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));   
   }

3. Delete all option option 
function removeAll(){
         var obj=document.getElementById('mySelect');
  
         obj.options.length=0;  

   }

4. Option to delete an 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);  
   }


5. To obtain the option value 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].value;


6. To obtain a copy option 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].text;


7. Edit Options 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);


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