<select>标签
选择事件:onchange
获取选中值:
alert(city.options[this.selectedIndex].value);
获取选中文本
alert(city.options[this.selectedIndex].text);
设置选中项
city.selectedIndex=3;
判断是否被选中
alert(city.options[1].selected);
添加选项
varcity=document.getElementById("city");
varoption=newOption("大连","dalian");
city.add(option,0);
删除选项
city.remove(0);
