JavaScript实现无穷滚动加载数据

首先实现滚动要借助onscroll事件处理程序。

无穷滚动就是滑动滚动条，实现数据块的无穷加载。

我们以瀑布流的布局来实现无穷加载。瀑布流就是一些等宽不等高的数据块布局。在滚动条下拉时，它会进行加载。那么问题就是在判断什么时候应该加载。

我们首先应该明白瀑布流布局的特点。它将下一个图片总是放在当前列数最低的那一列。所以当加载最后一个蓝色的图片时，也就无疑是最后一个图片了。所以要判断该图片加载到什么程度来触发滚动事件。
图上灰色的表示页面的大小，后面蓝色边框表示窗口的大小。当拖动滚动条时，灰色部分上移。我们希望页面最后一个图片（蓝色图片）加载一半时触发滚动事件。那么就要形成参照。

下来写代码：

//检测是否具备滚动条加载数据块的条件
function checkScrollSlide(){
 var oparent = document.getElementById('main');
 var oBoxs = getByClass(oparent,'box');
 var scrollH = document.body.scrollTop || document.documentElement.scrollTop + document.body.clientHeight || document.documentElement.clientHeight;
 var lastBoxH = oBoxs[oBoxs.length - 1].offsetTop + Math.floor(oBoxs[oBoxs.length - 1].offsetHeight/2);

 return (lastBoxH < scrollH )? true : false;
}

getClass是根据类名查找元素集合的自己写的函数，待会儿会附上源码

我们要进行加载的数据块的格式是这样的.每个图片被一个class= pic的div包裹。最后整体属于父元素main

<div id = "main">
 <div class = "box">
  <div class = "pic">
   <img src = "images/0.jpg">
  </div>
 </div>
 <div class = "box">
  <div class = "pic">
   <img src = "images/1.jpg">
  </div>
 </div>
 <div class = "box">
  <div class = "pic">
   <img src = "images/2.jpg">
  </div>
 </div>
<div>

首先我们要加载的数据块应该是从后台传过来的，在这里我们用json模拟一下就可以：

var DataIn = {"data":[{"src":'0.jpg'},{"src":'1.jpg'},{"src":'2.jpg'},{"src":'3.jpg'},{"src":'4.jpg'},{"src":'5.jpg'}]};

比如这个就是后台传过来的数据。

上面的函数返回一个布尔值，当为true时，触发滚动事件。

 window.onscroll = function(){
 var oparent = document.getElementById('main');
 //当满足加载条件时，就要向页面中加载数据块
 if(checkScrollSlide){
  for(var i = 0; i< DataIn.data.length; i++){
    var oBox = document.createElement('div');
    oBox.className = 'box';
    oparent.appendChild(oBox);

    var opic = document.createElement('div');
    opic.className = 'pic';
    oBox.appendChild(opic);

    var oImg = document.createElement('img');
    oImg.src = './images/'+DataIn.data[i].src;
    opic.appendChild(oImg);

   }
   waterFull('main','box');
  }
 }
}

附上源码：

css和html

<!DOCTYPE html>
<html>
<head>
<meta charset = "utf-8" />
<script src = "./jswaterfll.js"></script>
 <title>瀑布流布局</title>
 <style type="text/css">
 *{
 padding: 0px;
 margin: 0px;
 }

 #main{
 position: relative;

 }
 .box{
/* display: inline-block;*/
 padding: 15px 0px 0px 15px;
 float: left;

 }
 .pic{
 padding: 10px;
 border-radius: 5px;
 border:1px solid #ccc;
 box-shadow: 0 0 5px #ccc;
 }

 .pic img{
 width: 165px;
 height: auto;
 }
 </style>
</head>
<body>
<div id = 'main'>
 <div class = "box">
 <div class = "pic">
  <img src = "images/3.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/4.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/20.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/21.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/2.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/3.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/4.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/5.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/6.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/7.jpg">
 </div>
 </div>

 <div class = "box">
 <div class = "pic">
  <img src = "images/8.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/9.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/10.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/11.jpg">
 </div>
 </div>

 <div class = "box">
 <div class = "pic">
  <img src = "images/17.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/18.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/19.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/4.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/5.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/6.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/7.jpg">
 </div>
 </div>

 <div class = "box">
 <div class = "pic">
  <img src = "images/8.jpg">
 </div>
 </div>

 <div class = "box">
 <div class = "pic">
  <img src = "images/11.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/12.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/13.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/14.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/15.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/16.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/17.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/18.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/19.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/20.jpg">
 </div>
 </div>
 <div class = "box">
 <div class = "pic">
  <img src = "images/21.jpg">
 </div>
 </div>
</div>
</body>
</html>

js代码：

window.onload = function(){
 waterFull('main','box');

 var DataIn = {"data":[{"src":'0.jpg'},{"src":'1.jpg'},{"src":'2.jpg'},{"src":'3.jpg'},{"src":'4.jpg'},{"src":'5.jpg'}]};
 window.onscroll = function(){
  var oparent = document.getElementById('main');
  if(checkScrollSlide){
   for(var i = 0; i< DataIn.data.length; i++){
    var oBox = document.createElement('div');
    oBox.className = 'box';
    oparent.appendChild(oBox);

    var opic = document.createElement('div');
    opic.className = 'pic';
    oBox.appendChild(opic);

    var oImg = document.createElement('img');
    oImg.src = './images/'+DataIn.data[i].src;
    opic.appendChild(oImg);

   }
   waterFull('main','box');
  }
 }
}

function waterFull(parent,children){
 var oParent = document.getElementById(parent);
 //var oBoxs = parent.querySelectorAll(".box");

  var oBoxs = getByClass(oParent,children);

 //计算整个页面显示的列数

 var oBoxW = oBoxs[0].offsetWidth;

 var cols = Math.floor(document.documentElement.clientWidth/oBoxW);

 //设置main的宽度，并且居中

 oParent.style.cssText = 'width:'+oBoxW * cols +'px; margin: 0 auto';

 //找出高度最小的图片，将下一个图片放在下面

 //定义一个数组，存放每一列的高度，初始化存的是第一行的所有列的高度

 var arrH = [];

 for(var i = 0; i< oBoxs.length ; i++){
  if(i < cols){
   arrH.push(oBoxs[i].offsetHeight);
  }
  else{
   var minH = Math.min.apply(null,arrH);

   var minIndex = getMinhIndex(arrH,minH);

   oBoxs[i].style.position = 'absolute';
   oBoxs[i].style.top= minH + 'px';
   //oBoxs[i].style.left = minIndex * oBoxW + 'px';
   oBoxs[i].style.left = oBoxs[minIndex].offsetLeft+'px';

   arrH[minIndex] += oBoxs[i].offsetHeight;
  }
 }

}
function getByClass(parent,className){

 var boxArr = new Array();//用来获取所有class为box的元素

 oElement = parent.getElementsByTagName('*');

 for (var i = 0; i <oElement.length; i++) {

  if(oElement[i].className == className){

   boxArr.push(oElement[i]);

  }
 };
 return boxArr;
}

//获取当前最小值得下标
function getMinhIndex(array,min){

 for(var i in array){

  if(array[i] == min)

   return i;
 }
}

//检测是否具备滚动条加载数据块的条件
function checkScrollSlide(){
 var oparent = document.getElementById('main');
 var oBoxs = getByClass(oparent,'box');
 var scrollH = document.body.scrollTop || document.documentElement.scrollTop + document.body.clientHeight || document.documentElement.clientHeight;
 var lastBoxH = oBoxs[oBoxs.length - 1].offsetTop + Math.floor(oBoxs[oBoxs.length - 1].offsetHeight/2);

 return (lastBoxH < scrollH )? true : false;
}

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