JS实现图片懒加载插件

    <ul class="container">
        <li><img src="img/timg.gif" alt="1" lazyImg-src="img/1.jpg"></li>
        <li><img src="img/timg.gif" alt="2" lazyImg-src="img/2.jpg"></li>
        <li><img src="img/timg.gif" alt="3" lazyImg-src="img/3.jpg"></li>
        <li><img src="img/timg.gif" alt="4" lazyImg-src="img/4.jpg"></li>
        <li><img src="img/timg.gif" alt="5" lazyImg-src="img/5.jpg"></li>
        <li><img src="img/timg.gif" alt="6" lazyImg-src="img/6.jpg"></li>
        <li><img src="img/timg.gif" alt="7" lazyImg-src="img/7.jpg"></li>
        <li><img src="img/timg.gif" alt="8" lazyImg-src="img/8.jpg"></li>
        <li><img src="img/timg.gif" alt="9" lazyImg-src="img/9.jpg"></li>
        <li><img src="img/timg.gif" alt="10" lazyImg-src="img/10.jpg"></li>
    </ul>

body{
    position:relative;
    padding:0;
    margin:0;
    display: table;
}
.container{
    list-style: none;
    height: 400px;
    width: 250px;
    overflow: auto;
    margin-top:200px;
}
.container>li{
    margin-bottom: 10px;
}
.container>li>img{
    background-color: #e4393c;
    width: 200px;
    height: 200px;
}

//处理图片懒加载
function lazyload (option) {
  //如果不传递视图对象，则默认视图对象为window
  var viewDom = option || window,
      scroll_top, //滚动条Y轴距离
      scroll_left, //滚动条X轴距离
      viewDomWidth, //视图宽
      viewDomHeight,//视图高
      viewDomLeft, //视图左偏移量
      viewDomTop, //视图上偏移量
      imgWidth, //img宽
      imgHeight, //img高
      imgLeft, //img左偏移量
      imgTop, //img上偏移量
      imgArr = [],
      doc = document.documentElement;

  //获取视图元素宽高,左上偏移量，分为window或普通dom两种情况
  if (viewDom === window) {
    viewDomWidth = doc.clientWidth; 
    viewDomHeight = doc.clientHeight;
    viewDomLeft = doc.offsetLeft;
    viewDomTop = doc.offsetTop;
  }else{
    viewDomWidth = viewDom.offsetWidth;
    viewDomHeight = viewDom.offsetHeight;
    viewDomLeft = viewDom.offsetLeft;
    viewDomTop = viewDom.offsetTop;
  };

  /**
   * @desc 将nodeList转为数组，方便操作
   * @param {object} data nodelist对象
   */
  function nodeListToArr(data) {
    var arr = [];
    try{
      //ie8及以下不支
      arr = Array.prototype.slice.call(data);
    }catch(e){
      //兼容写法
      var len = data.length;
      for(var i = 0; i < len; i++){
        arr.push(data[i]);
      }
    };
    return arr;
  };
  //取得所有需要懒加载的dom元素
  var imgNode = document.querySelectorAll("[lazyImg-src]");
  imgArr = nodeListToArr(imgNode);
  //替换路径函数,懒加载核心函数
  function replaceUrl () {
    //只有img数组不为空，才会执行替换路径的操作
    if(imgArr.length){
      var i = 0;
      //获取视图元素滚动条滚动距离
      if (viewDom === window) {
        scroll_top = doc.scrollTop;
        scroll_left = doc.scrollLeft;
      }else{
        scroll_top = viewDom.scrollTop;
        scroll_left = viewDom.scrollLeft;
      };
      //遍历需要懒加载的dom节点
      for (; i<imgArr.length; i++) {
        //获取当前元素的宽高
        imgWidth = imgArr[i].offsetWidth;
        imgHeight = imgArr[i].offsetHeight;
        //当前元素随着滚动的变化的偏移量为
        imgLeft = imgArr[i].offsetLeft - scroll_left;
        imgTop = imgArr[i].offsetTop - scroll_top;
        //横向判断是否进入视图元素
        var boundaryLeft = imgLeft + imgWidth - viewDomLeft;
        var boundaryRight = viewDomLeft + viewDomWidth - imgLeft;
        //同理纵向判断是否进入视图元素
        var boundaryTop = imgTop + imgHeight - viewDomTop;
        var boundaryBottom = viewDomTop + viewDomHeight - imgTop;
        if(boundaryLeft>0 && boundaryRight>0 && boundaryTop>0 && boundaryBottom>0) {
          //替换图片路径,添加判断，img替换src，非img替换background
          if(imgArr[i].nodeName === "IMG"){
            imgArr[i].src = imgArr[i].attributes['lazyimg-src'].value;
          }else{
            //不是图片的替换背景图
            // imgArr[i].style.backgroundImage = imgArr[i].attributes['lazyimg-src'].value;
          };
          //操作完一项就删除一项，同时重置i;
          imgArr.splice(i,1);
          i -= 1;
        };
      };
    };
  };
  //自调
  replaceUrl();
  //添加事件监听
  viewDom.addEventListener("scroll",replaceUrl);
};
//测试调用，默认绑定window，或传递你需要监听的dom对象，调用就2步
var container = document.querySelector(".container");
lazyload(container);