直接上代码   ：

var imageitem;
    var imageitemstring=‘‘;
    for(var i=0;i< that.data.fbimages.length;i++)
    {
      imageitem=‘{"fileUrl":"‘+ that.data.fbimages[i] +‘"}‘;
      if(i<that.data.fbimages.length-1)
      {imageitemstring += imageitem + ‘,‘;}
      else{imageitemstring += imageitem}
    }
    var imageList=‘{"imageList":[‘+imageitemstring+‘]}‘;

fbimages为fileURL文件路径的数组；最终格式化的数据为：

{"imageList":[{"fileUrl":"http://218.87.254.137:7999/uploads/20170528/48e11aa9-88ef-449e-b617-513c83a09f40.jpg"},{"fileUrl":"http://218.87.254.137:7999/uploads/20170528/4050ceaa-1673-42e8-97ea-56991290ad76.png"},{"fileUrl":"http://218.87.254.137:7999/uploads/20170528/59403872-0f18-43a6-93e4-53a0816bd047.jpg"}]}

微信小程序开发之拼接json数组字符串