二级联动

创建一级select标签，将标签添加到HTML上

var select = document.createElement('select');
select.setAttribute('id','sel');
document.body.appendChild(select);

创建二级select标签

var select1 = document.createElement('select');
document.body.appendChild(select1);

创建一级请选择option标签

var xuanze = document.createElement('option');        
xuanze.innerHTML = '请选择';        
select.appendChild(xuanze);

创建二级请选择option标签

var xuanze1 = document.createElement('option');        
xuanze1.innerHTML = '请选择';        
select1.appendChild(xuanze1);

循环获取每个省，并将名称添加到option上

for(var i = 0;i < city_data.length;i++){            
var option = document.createElement('option');            
option.innerHTML = city_data[i].city;
select.appendChild(option);        
}

获取select的id

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

获取每个省下面的市

sel.onchange = function(){
select1.options.length = 1;
if(this.selectedIndex - 1 > -1){
for(var i = 0;i < city_data[this.selectedIndex - 1]['area'].length;i++){
var option1 = document.createElement('option');
option1.innerHTML = city_data[this.selectedIndex - 1]['area'][i];                    select1.appendChild(option1);
}            
}        
}