<script type="text/javascript">//得到选中项的索引，文本和值函数function getselected(selectedIndex){var selectbox=document.forms[0].elements["location"];var index=selectbox[selectedIndex];var selectedOption=selectbox.options[selectedIndex];console.log("索引："+index.index +" 文本："+selectedOption.text+" 值："+selectedOption.value);}//设置选中项function setOpionSelected(index){var selectbox=document.forms[0].elements["location"];selectbox[index].selected=true;}setOpionSelected(3);//得到选中项的元素function getSelectdOptions(selectbox){var result=new Array();var option=null;for(var i=0,len=selectbox.options.length;i<len;i++){option=selectbox.options[i];if(option.selected){result.push(option);}}return result;}var selected=document.forms[0].elements["location"];//console.log(getSelectdOptions(selected).pop().index);//创建option,这种是用节点的方式var newOption=document.createElement("option");newOption.appendChild(document.createTextNode("option text"));newOption.setAttribute("value","Option value");selected.appendChild(newOption);//创建option,这种是用option对象创建，再用add()函数添加节点，inserBefore()是选择插入位置，如果是插入到最后第2参数直接用"undefined"即可var newOption=new Option("option text","option value");selected.add(newOption,selected.insertBefore(newOption,selected.options[1]));</script>

//html部分

<div id="container"><form action="#" method="post" id="login"><select name="location" id="sel"><option value="sunnyvale, CA">Sunnyvale</option><option value="Los Angeles,CA">Los Angeles</option><option value="Mountain View,CA">Mountain View</option><option value="">China</option><option >Australia</option></select></form></div>