js二级联动

  var str={
  "广东":["汕头","揭阳","潮州"],
  "福建":["福州","龙岩","莆田"]
  }

 for(var key in str){
    var optionz=document.createElement("option");
    optionz.text = key;//text显示,显示key的值
    optionz.value = key;//给下面取值
    province.options.add(optionz);
   }
   //第一个下拉框的值改变时,第二个下拉框跟着变化;,级联
  province.onchange = function(){
   city.innerHTML="";
   var arr = str[this.value];//通过value取值
   for(var i=0;i<arr.length;i++){
    var optionz=document.createElement("option");
    optionz.text = arr[i];
    optionz.value = arr[i];
    city.appendChild(optionz);
   }
  }