<select onchange="isSelected(this.value);" id="city">
<option value="1">北京</option>
<option value="2" >上海</option>
<option value="2" >廣州</option>
</select>

function isSelected(value) {
var cityName;
var city = document.getElementById("city");
//獲取選中的城市名稱
for(i=0;i<city.length;i++){
if(city[i].selected==true){
cityName = city[i].innerText; //關鍵點
alert("cityName:" + cityName);
}
}

function isSelected(value) {
var city = document.getElementById("city");
alert(city.options[city.selectedIndex].innerText);
}