1 var select= document.getElementById("selectid");
2 var objOption = document.createElement("OPTION");
3 objOption.value = value;
4 objOption.text =text;
5 select.add(objOption);

 获取select选中值

var index=document.getElementById("selectid").selectedIndex;
var text=document.getElementById("selectid").options[index].text;
var val=document.getElementById("selectid").options[index].value;