ajax请求？返回数据处理？怎么是空数据？

Question

$.ajax({

    type:'POST',

     dataType: "json",

     url:"url",

     data:adata,

    success:function(data){

        console.log(data);

        var arr=[];

        for(var i in data){

            arr.push(data[i])

        }

        var str='';

        for(j=0;j<arr[2].length;j++){

              str+='<div class="question1">';

              str+='<p>'+arr[2][j].question+'</p>';

               str+='<ul>';

               str+='<li class="jjjj" value="A">'+arr[2][j].answera+'</li>';  

               str+='<li class="jjjj" value="B">'+arr[2][j].answerb+'</li>';

               str+='<li class="jjjj" value="C">'+arr[2][j].answerc+'</li>';

               str+='<li class="jjjj" value="D">'+arr[2][j].answerd+'</li>';  

               str+='</ul>';

               str+='</div>';   

        }

        $("#container").html(str);

这是我请求到的数据 和前端渲染，但是后台返回我的数据有时候是三个选项，有时是四个选项，我现在的处理方法就会还是四个选项，但是有一个undefind,怎么处理，求大神帮忙

Answer 1

判断下 d 是否存在for(j=0;j<arr[2].length;j++){&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; str+='<div class="question1">';&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; str+='<p>'+arr[2][j].question+'</p>';&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;str+='<ul>';&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;str+='<li class="jjjj" value="A">'+arr[2][j].answera+'</li>';&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;str+='<li class="jjjj" value="B">'+arr[2][j].answerb+'</li>';&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;str+='<li class="jjjj" value="C">'+arr[2][j].answerc+'</li>';&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;if(arr[2][j].answerd){&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;str+='<li class="jjjj" value="D">'+arr[2][j].answerd+'</li>';&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;}&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;str+='</ul>';&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;str+='</div>';&nbsp; &nbsp;&nbsp; &nbsp; &nbsp; &nbsp; }

Answer 2

if(arr[2][j].answerd != undefined)str+='<li class="jjjj" value="D">'+arr[2][j].answerd+'</li>';

Answer 3

我觉得这个就是接口没处理好, 选项就该用数组返回!