javascript图片延迟加载实现方法及思路

  /
    @description: 返回浏览器的可视区域位置
    @return: left:左滑轮距离，上滑轮距离，width可见区域宽度，height可见区域长度
   /
   function getClient(){
    var l,t,w,h;
    l = document.documentElement.scrollLeft||document.body.scrollLeft;
    t = document.documentElement.scrollTop||document.body.scrollTop;
    w = document.documentElement.clientWidth;
    h = document.documentElement.clientHeight;
    return {left:l,:t,width:w,height:h};
   }

/
    @description: 返回待加载资源位置
    @params: p:需要加载的资源节点
    @return: left:左边距离，上边距离，width宽度，height高度
   /
   function getSubClient(p){
    var l = 0, t = 0, w, h;
    w = p.offsetWidth;
    h = p.offsetHeight;
    while(p.offsetParent){
      l += p.offsetLeft;
      t += p.offsetTop;
      p = p.offsetParent;
    } 
    return {left:l,:t,width:w,height:h};
   }

  /
    @decription: 判断两个矩阵是否相交，返回一个布尔值
    @params: rec1,rec2:需要比较的节点矩阵
    @return: true 两矩阵相交
   /
   function contains(rec1,rec2){
    var lc1,lc2,tc1,tc2,w1,h1;
    lc1 = rec1.left + rec1.width/2;
    lc2 = rec2.left + rec2.width/2;
    tc1 = rec1. + rec1.height/2;
    tc2 = rec2. + rec2.height/2;
    w1 = (rec1.width + rec2.width)/2;
    h1 = (rec1.height + rec2.height)/2;
    return Math.abs(lc1 - lc2)<w1&&Math.abs(tc1 - tc2)<h1;
   }

   /
    @description: 资源出现在视野中再加载.将资源放入一个数组。
   /
   var arr = document.getElementsByClassName("divX");
   window.onscroll = function(){
    var prec1 = getClient();
    var prec2;
    for(var i = arr.length-1;i>=0;i--){
      if(arr[i]){
        prec2 = getSubClient(arr[i]);
        if(contains(prec1,prec2)){
          //加载资源
          console.log(arr[i].id);
          arr[i].childNodes[0].src = arr[i].childNodes[0].getAttribute("lazy_src");
          delete arr[i];
        }
      }
    }
   }

 function imgLoad(img, callback) {
      var timer = setInterval(function() {
        if (img.plete) {
          callback(img)
          clearInterval(timer)
        }
      }, 50)
    }
    imgLoad(img1, function() {
      p1.innerHTML('加载完毕')
    })

function include_js(file) {
  var _doc = document.getElementsByTagName('head')[0];
  var js = document.createElement('script');
  js.setAttribute('type', 'text/javascript');
  js.setAttribute('src', file);
  _doc.appendChild(js);
  if (!/@_on!@/0) { //if not IE
    //Firefox2、Firefox3、Safari3.1+、Opera9.6+ support js.onload
    js.onload = function () {
      alert('Firefox2、Firefox3、Safari3.1+、Opera9.6+ support js.onload');
    }
  } else {
    //IE6、IE7 support js.onreadystatechange
    js.onreadystatechange = function () {
      if (js.readyState == 'loaded' || js.readyState == 'plete') {
        alert('IE6、IE7 support js.onreadystatechange');
      }
    }
  }
  return false;
}