//1.判断select选项中 是否存在Value="paraValue"的Item
function jsSelectIsExitItem(objSelect,objItemValue)
{
var isExit = false;
for(var i=0;i<objSelect.options.length;i++)
{
if(objSelect.options[i].value == objItemValue)
{
isExit = true;
break;
}
}
return isExit;
}

http://www.corange.cn/archives/2008/10/2113.html