jQuery实现图片预加载与懒加载功能详解

$(function(){
   loadImg("http://d.hiphotos.baidu.com/image/pic/item/fd039245d688d43f14f69eff7f1ed21b0ef43b5b.jpg",addImg);
  function loadImg(url,callback){
    var img = new Image();
    img.onload = function(){
      img.onload = null;
      callback(img);
    }
    img.src=url;
    img.width ="202";
    img.height = "202";
    img.attr("defaulturl","../images/img.png");
    if(){}
  }
  function addImg(img){
    $(img).appendTo($(".imgload li"))
  }
})

<!doctype html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>图片预加载</title>
  <link rel="stylesheet" type="text/css" href="css/index.css">
  <script type="text/javascript" src="js/jquery-1.8.3.min.js"></script>
  <script type="text/javascript" src="js/index.js"></script>
</head>
<body>
   
    <div class="imgload">
      <ul>
          <li class="fl"></li>
          <li class="fl"></li>
          <li class="fl"></li>
          <li class="fl"></li>
          <li class="fl"></li>
          <li class="fl"></li>
          <li class="fl"></li>
          <li class="fl"></li>
          <li class="fl"></li>
      </ul>
    </div>
</body>
</html>

function loadimg(arr,funLoading,funOnLoad,funOnError){ 
  var numLoaded=0, 
  numError=0, 
  isObject=Object.prototype.toString.call(arr)==="[object Object]" ? true : false; 
  
  var arr=isObject ? arr.get() : arr; 
  for(a in arr){ 
    var src=isObject ? $(arr[a]).attr("data-src") : arr[a]; 
    preload(src,arr[a]); 
  } 
  
  function preload(src,obj){ 
    var img=new Image(); 
    img.onload=function(){ 
      numLoaded++; 
      funLoading && funLoading(numLoaded,arr.length,src,obj); 
      funOnLoad && numLoaded==arr.length && funOnLoad(numError); 
    }; 
    img.onerror=function(){ 
      numLoaded++; 
      numError++; 
      funOnError && funOnError(numLoaded,arr.length,src,obj); 
    } 
    img.src=src; 
  } 
  
} 

var imgonload=function(errors){ 
    /*errors：加载出错的图片数量；*/ 
  console.log("loaded,"+errors+" images loaded error!"); 
} 
  
var funloading=function(n,total,src,obj){ 
    /* 
    n：已加载完成的数量； 
    total：总共需加载的图片数量； 
    src：当前加载完成的图片路径； 
    obj：当loadimg函数中传入的arr为存放图片路径的数组时，obj=src，是图片路径， 
        当arr为jquery对象时，obj是当前加载完成的img dom对象。 
    */ 
  console.log(n+"of"+total+" pic loaded.",src); 
  var newimg = document.createElement("img"); 
  newimg.src=src; 
  $("body").append(newimg).fadeIn(); 
} 
  
var funloading_obj=function(n,total,src,obj){ 
  console.log(n+"of"+total+" pic loaded.",src); 
  $(obj).attr("src",src); 
  $(obj).fadeIn(200); 
} 
  
var funOnError=function(n,total,src,obj){ 
  console.log("the "+n+"st img loaded Error!"); 
} 

console.log("loading..."); 
loadimg($("img"),funloading_obj,imgonload,funOnError); 
/*loadimg(["http://pic22.nipic.com/20120619/9607634_212642465144_2.jpg", 
     "http://pic21.nipic.com/20120531/1670912_103610084349_2.jpg", 
     "http://pic21.nipic.com/20120616/4952071_130629530136_2.jpg", 
     "http://pic21.nipic.com/20120610/1723580_105037029000_2.jpg", 
     "http://pic22.nipic.com/20120617/2572038_125013326121_2.jpg" 
    ],funloading,imgonload,funOnError);*/