jQuery AJAX实现点击加载更多图片及预加载效果

HTML结构与样式定义

<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <title>ajax点击加载更多数据--博客园--勇淘未来</title>
    <script type="text/javascript" src="jquery-1.11.1.min.js"></script>
    <style>
      *{padding:0;margin:0;}
      .box {margin: 100px auto;width: 550px;}
      ul li {width:550px;list-style: none;}
      ul li span{text-align:center;display:block;}
      .clear {clear: both;}
      .load {text-align: center;display: none;margin-top:50px;color:#ccc;}
      .end{display:none;color:#ccc;}
    </style>
  </head>
  <body>
    <div class="box">
      <ul></ul>
      <div class="clear"></div>
      <div class="load">加载中...</div>
      <div class="more" style="text-align: center;margin-top:50px;">
        <button class="btn">查看更多图片</button>
        <div class="end">没有更多了</div>
      </div>
    </div>
    <script>
      var num = 0;
      var start = 0;
      var size = 2;
      $.ajax({
        url: "dataNews.json",
        type: "get",
        success: function(res){
          var str = "";
          for(var i = 0;i < 2;i++){
            str += "<li><img src=" + res[i].img + "><span>"+ res[i].title +"</span></li>";
          }
          $(".box ul").append(str);
        },
        error:function(){
          console.log(errors);
        }
      })
      $(".btn").click(function(){
        $(".load").show();
        setTimeout(function(){
          $(".load").hide();
          num++;
          console.log(num);
          start = num * size;
          $.ajax({
            url:"dataNews.json",
            type:"get",
            success:function(res){
              var sum = res.length;
              if(start + size > sum) {
                size = sum - start;
                $(".btn").css("display","none");
                $(".end").css("display","block");
              }
              var str = "";
              for(var i = start;i<(start + size);i++) {
                str += "<li><img src=" + res[i].img + "><span>"+ res[i].title +"</span></li>";
              }
              console.log(start + size);
              $("ul").append(str);
            }
          });
        },300)
      }
    )
    </script>
</body>
</html>

[ {
  "img":"img/sina.jpg","title":"百度音乐1"
}
, {
  "img":"img/tengxu.jpg","title":"百度音乐2"
}
, {
  "img":"img/sina.jpg","title":"百度音乐3"
}
, {
  "img":"img/tengxu.jpg","title":"百度音乐4"
}
, {
  "img":"img/tengxu.jpg","title":"百度音乐5"
}
, {
  "img":"img/sina.jpg","title":"百度音乐6"
}
, {
  "img":"img/tengxu.jpg","title":"百度音乐7"
}
, {
  "img":"img/sina.jpg","title":"百度音乐8"
}
, {
  "img":"img/tengxu.jpg","title":"百度音乐9"
}
, {
  "img":"img/sina.jpg","title":"百度音乐10"
}
, {
  "img":"img/tengxu.jpg","title":"百度音乐11"
}
, {
  "img":"img/sina.jpg","title":"百度音乐12"
}
, {
  "img":"img/tengxu.jpg","title":"百度音乐13"
}
, {
  "img":"img/sina.jpg","title":"百度音乐14"
}
, {
  "img":"img/tengxu.jpg","title":"百度音乐15"
}
]