老师帮忙详解一下代码

function address(){

    /*请在此补充代码*/

    var sheng=document.getElementById("sheng"); 

    var shi=document.getElementById("shi"); 

    var Obj1=["北京市","天津市","河北省","河南省"];

    var Obj2=["朝阳区","西城区","石家庄","秦皇岛","邯郸市","洛阳市","郑州市","商丘市"]

    selectAdd(sheng,Obj1);

    selectAdd(shi,Obj2);

}

function selectAdd(obj,name,value){

/*请在此补充代码*/

for(var value in name){

obj.options.add(new Option(name[value]));

}

function selectAdd(obj,name,value)这个