原生ajax瀑布流demo分享(必看篇)

?php
　　//模拟从数据库读取数据
  $arr = array();
  $op = opendir('./img');  //打开目录

  //循环读取目录
  while (($file = readdir($op)) !== false) {
    //过滤点和点点
    if ($file == '.' || $file == '..') {
      continue;
    }
    $arr[] = $file;
  }
  closedir($op);  //关闭目录
  echo json_encode($arr);

!DOCTYPE html>
html lang="en">
head>
  meta charset="UTF-8">
  title>瀑布流/title>
  style>
    li{
      list-style: none;
      float: left;
      margin:4px;
    }
    img{
      border:4px solid black;
    }
  /style>
/head>
body>
  ul id="ul">
    !-- li>img src="./img/1.jpg" height="300" alt="">/li> -->
  /ul>
/body>
script>
  //找对象
  var ul = document.getElementById('ul');

  //拿数据
  function getData()
  {
    var ajax = new XMLHttpRequest();
    ajax.open('get', 'ajax.php', true);
    ajax.send();
    ajax.onreadystatechange = function()
    {
      if (ajax.readyState == 4  ajax.status == 200) {
        var res = ajax.responseText;
        //处理结果
        var obj = JSON.parse(res);
        for (var k in obj) {
          // obj[k];
          //创建节点
          var li = document.createElement('li');
          li.innerHTML = 'img src="./img/'+obj[k]+'" height="300" />';
          ul.appendChild(li);
        }
      }
    }
  }
  getData();

  var timer;
  //判断滚动条的高度，加载第二批文件
  window.onscroll = function()
  {
    //获取三高
    var zGao = document.documentElement.scrollHeight;//总高度
    var lGao = document.documentElement.clientHeight;//浏览器可用高度
    var gGao = document.body.scrollTop || document.documentElement.scrollTop;//滚出去的高度
    // console.log(zGao, lGao, gGao);

    document.title = zGao + '_' + lGao + '_' + gGao;

    if (zGao - lGao - gGao  500) {
      clearTimeout(timer);
      //用一次性定时器解决连续加载的问题
      timer = setTimeout(function(){
        getData();
      }, 200)
    }
  }
/script>
/html>