给select添加自定义值和选项
添加选项:
document.getElementById("id_select").options.add(new Option("name", "value"));
添加自定义的myVal值"value1"
document.getElementById("id_select").options[0].setAttribute("myVal", "value1");
获取自定义的myVal的值
document.getElementById("id_select").options[0].getAttribute("myVal");