Analyze the principle of javascript waterfall flow to achieve scrolling loading of images

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Analyze the principle of javascript waterfall flow to achieve scrolling loading of images_javascript skills

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May 16, 2016 pm 03:11 PM

Let’s learn about waterfall flow first

Waterfall flow, also known as waterfall flow layout. It is a popular website page layout. The visual performance is a jagged multi-column layout. As the page scroll bar scrolls down, this layout will continuously load data blocks and append them to the current tail. The first website to adopt this layout was Pinterest, which gradually became popular in the country. Most of the fresh websites in China basically use this style, such as Meilishuo and Taobao.

This is an effect I achieved, that is, it won’t load no matter how I scroll. Just flow and flow like a waterfall!

We only talk about the Js implementation method here

Implementation principle:

Calculate for the first time the existing data block elements in the container: 1. Total width of the container 2. Column width 3. Minimum number of columns. After getting the number of columns, use an array to store all the heights of the box to find the minimum height. Then the height is updated based on the serial number; it seems a bit awkward, but it is very simple to implement.

For scrolling loading: that is, after scrolling to a height, you need to load data. In fact, this is the minimum height value of the column. In this way, comparing the current scroll value with the minimum height value can determine whether to trigger loading of data; that is Write a function to determine whether the conditions for loading images are met. If so, start loading. For example, get the offsetTop, visual area height, and scrolling distance of the last picture. That is, when the offsetTop of the picture is less than the sum of the visual area height and the scrolling distance, it should be loaded at this time, but the conditions can be determined arbitrarily. You can also wait until the picture is halfway scrolled before triggering the loading condition, as shown in the picture:

Enter the HTML CSS code first

<!DOCTYPE html>
<html lang="en">
<head>
 <meta charset="UTF-8">
 <title>waterfall</title>
 <script src="script.js"></script>
 <style>
  * {
   margin: 0;
   padding: 0;
  }
  body {
   background: yellow;
  }
  #container {

  }
  #container .pin {
   padding-left: 15px;
   padding-top: 15px;
   float: left;
  }
  #container .div-box {
   float: left;
   border: 1px solid #ccc;
   box-shadow: 0 0 5px #bbb;
   background: #fff;
   padding: 12px;
   border-radius: 9px;
  }
  #container .div-box img {
   width: 300px;
  }
  #container .div-box p {
   text-align: center;
   font-size: 20px;
   font-weight: bold;
   color: red;
  }
 </style>
 <script>
  
 </script>
</head>
<body>
 <div id="container">
  <div class="pin">
   <div class="div-box">
    <img src="/static/imghwm/default1.png"  data-src="img/1.jpg"  class="lazy" alt="">
    <p>白超华-博客园</p>
   </div>
  </div>
  <div class="pin">
   <div class="div-box">
    <img src="/static/imghwm/default1.png"  data-src="img/2.jpg"  class="lazy" alt="">
    <p>白超华-博客园</p>
   </div>
  </div>
  <div class="pin">
   <div class="div-box">
    <img src="/static/imghwm/default1.png"  data-src="img/3.jpg"  class="lazy" alt="">
    <p>白超华-博客园</p>
   </div>
  </div>
  <div class="pin">
   <div class="div-box">
    <img src="/static/imghwm/default1.png"  data-src="img/4.jpg"  class="lazy" alt="">
    <p>白超华-博客园</p>
   </div>
  </div>
  <div class="pin">
   <div class="div-box">
    <img src="/static/imghwm/default1.png"  data-src="img/5.jpg"  class="lazy" alt="">
    <p>白超华-博客园</p>
   </div>
  </div>
  <div class="pin">
   <div class="div-box">
    <img src="/static/imghwm/default1.png"  data-src="img/6.jpg"  class="lazy" alt="">
    <p>白超华-博客园</p>
   </div>
  </div>
  <div class="pin">
   <div class="div-box">
    <img src="/static/imghwm/default1.png"  data-src="img/7.jpg"  class="lazy" alt="">
    <p>白超华-博客园</p>
   </div>
  </div>
  <div class="pin">
   <div class="div-box">
    <img src="/static/imghwm/default1.png"  data-src="img/8.jpg"  class="lazy" alt="">
    <p>白超华-博客园</p>
   </div>
  </div>
  <div class="pin">
   <div class="div-box">
    <img src="/static/imghwm/default1.png"  data-src="img/9.jpg"  class="lazy" alt="">
    <p>白超华-博客园</p>
   </div>
  </div>
  <div class="pin">
   <div class="div-box">
    <img src="/static/imghwm/default1.png"  data-src="img/10.jpg"  class="lazy" alt="">
    <p>白超华-博客园</p>
   </div>
  </div>
  <div class="pin">
   <div class="div-box">
    <img src="/static/imghwm/default1.png"  data-src="img/1.jpg"  class="lazy" alt="">
    <p>白超华-博客园</p>
   </div>
  </div>
  <div class="pin">
   <div class="div-box">
    <img src="/static/imghwm/default1.png"  data-src="img/2.jpg"  class="lazy" alt="">
    <p>白超华-博客园</p>
   </div>
  </div>
  <div class="pin">
   <div class="div-box">
    <img src="/static/imghwm/default1.png"  data-src="img/3.jpg"  class="lazy" alt="">
    <p>白超华-博客园</p>
   </div>
  </div>
  <div class="pin">
   <div class="div-box">
    <img src="/static/imghwm/default1.png"  data-src="img/4.jpg"  class="lazy" alt="">
    <p>白超华-博客园</p>
   </div>
  </div>
  <div class="pin">
   <div class="div-box">
    <img src="/static/imghwm/default1.png"  data-src="img/5.jpg"  class="lazy" alt="">
    <p>白超华-博客园</p>
   </div>
  </div>
  <div class="pin">
   <div class="div-box">
    <img src="/static/imghwm/default1.png"  data-src="img/6.jpg"  class="lazy" alt="">
    <p>白超华-博客园</p>
   </div>
  </div>
 </div>
</body>
</html>

JS code, each line has comments

window.onload = function(){
 var data = {     //模拟后台数据 的一个JSON格式的文件
  "data":[
   {"src":"1.jpg"},
   {"src":"2.jpg"},
   {"src":"3.jpg"},
   {"src":"4.jpg"},
   {"src":"5.jpg"},
  ]
 };
 window.onscroll = function(){
  if(checkScroll()){   //判断是否具备滚动加载得条件
   var oParent = document.getElementById('container');
   for(var i=0; i<data.data.length; i++){
    var div1 = document.createElement('div'); //创建div元素
    div1.className = 'pin';     //设置class
    oParent.appendChild(div1);
    var div2 = document.createElement('div');//创建div元素
    div2.className = 'div-box';
    div1.appendChild(div2);
    var imgs = document.createElement('img');//创建img元素
    imgs.style.width = '300px';
    imgs.src = 'img/'+data.data[i].src; //设置读取路径
    div2.appendChild(imgs);
    var p = document.createElement('p');//创建p元素
    p.innerHTML = '白超华-博客园';
    div2.appendChild(p);
   }
   waterfall('container','pin');  //--注意 别忘了这句，当滚动时候就执行
  }
 }
 waterfall('container','pin');
}
function waterfall(parent, box){
 var oParent = document.getElementById(parent);//获取父级对象
 var aBox = getByClass(oParent,box);//获取所有class为pin的盒子的集合
 var boxWidth = aBox[0].offsetWidth;//获取一个盒子的宽
 var pageWidth = document.body.clientWidth||document.documentElement.clientWidth;//获取可视区宽
 var cols = Math.floor(pageWidth/boxWidth);//获得列数
 var arrH = [];//用于存放盒子的高

 for(var i=0; i<aBox.length; i++){
  if(i<cols){//当小于第一列个数的时候
   arrH.push(aBox[i].offsetHeight);
  } else {
   var minH = Math.min.apply(null,arrH);//得到数组中盒字的最小高度minH;
   var index = getMinIndex(arrH,minH);

   aBox[i].style.position = 'absolute';//设置绝对定位
   aBox[i].style.top = minH+'px';//设置top，就是最小高度
   aBox[i].style.left = aBox[0].offsetWidth*index+'px';//设置left，就是一个盒子的宽*index索引数
   arrH[index]+=aBox[i].offsetHeight; //更新新添加盒字后的列高
  }
 }
}
//通过父级获取class
function getByClass(parent, classname){
 var aClass = parent.getElementsByTagName('*');
 var arr = [];

 for(var i=0; i<aClass.length; i++){
  if(aClass[i].className == classname){
   arr.push(aClass[i]);
  }
 }
 return arr;
}
//最小值的索引index
function getMinIndex(arr,val){
 for( i in arr){
  if(arr[i] == val){
   return i;
  }
 }
}
//
function checkScroll(){
 var oParent = document.getElementById('container');
 var aBox = getByClass(oParent,'pin');
 var lastBoxHeight = aBox[aBox.length-1].offsetTop;// 当滚到到这个距离时候就开始加载
 var scrollTop=document.documentElement.scrollTop||document.body.scrollTop;//兼容的滚动距离
 var documentHeight = document.documentElement.clientHeight; //页面高度
 if(lastBoxHeight<scrollTop+documentHeight){
  return true;
 }
}

The above is the entire content of this article, I hope it will be helpful to everyone’s study.

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