$.preloadImages = function () {
 for (var i = 0; i < arguments.length; i++) {
 $('img').attr('src', arguments[i]);
 }
};
$.preloadImages('img/hover-on.png', 'img/hover-off.png');

$('img[data]').load(function(){ 
 var __this__ = $(this); 
 var url = __this__.attr('data'); 
 var src = __this__.attr('src'); 
 if(url ==''|| url == src)//这里判断如果图片实际地址不存在或者已经加载不处理 
 { 
 return; 
 } 
 var img =newImage();//实例化一个图片的对象 
 img.src = url;//将要显示的图片加载进来 
 if(img.complete)//如果图片已经加载存在浏览器缓存中直接处理 
 { 
 __this__.attr('src',url);//将要显示的图片替换过来 
 return; 
 } 
 img.onload =function(){//要显示的图片加载完成后做处理 
 __this__.attr('src',url); 
 } 
}); 

var imgNum = 0;
var images = [];
$(function(){ preloadImg(); });
 
//里面有两种方式
function preLoadImg() {
 //第一种方式：通过dom方法获取页面中的所有img，包括<img>标签和css中的background-image
 /*get all imgs those tag is <img>
 var imgs = document.images;
 for (var i = 0; i < imgs.length; i++) {
 images.push(imgs[i].src);
 }
 //get all images in style
 var cssImages = getallBgimages();
 for (var j = 0; j < cssImages.length; j++) {
 images.push(cssImages[j]);
 }*/
 
 //第二种方式：把所有该网页上用到的图片文件都预先放入一个数组里 
 $.imgpreload(['images/bg1.jpg', 'images/bg2.jpg'], function () {
  //此处是显示进度百分比时需要用到的背景图，这个可以先加载进去
 });
 
 //then push all other images in array to load 
 images.push("images/test_1.png");
 images.push("images/test_2.png");
 images.push("images/test_3.png");
 //。。。
 images.push("images/test_n.png"); 
 
 /*这里是真正的图片预加载 preload*/
 $.imgpreload(images,
 {
 each: function () {
  /*this will be called after each image loaded*/
  var status = $(this).data('loaded') ? 'success' : 'error';
  if (status == "success") {  
  var v = (parseFloat(++imgNum) / images.length).toFixed(2);
  $("#percentShow").html(Math.round(v * 100) + "<sup>%</sup>");  
  }
 },
 all: function () {
  /*this will be called after all images loaded*/
  $("#percentShow ").html("100<sup>%</sup>");
 
  $("percentShow").fadeOut(1000);  
  $(".main").show();
 }
 });
}
 
//get all images in style（此方法引用其他博客的）
function getallBgimages() {
 var url, B = [], A = document.getElementsByTagName('*');
 A = B.slice.call(A, 0, A.length);
 while (A.length) {
 url = document.deepCss(A.shift(), 'background-image');
 if (url) url = /url\(['"]?([^")]+)/.exec(url) || [];
 url = url[1];
 if (url && B.indexOf(url) == -1) B[B.length] = url;
 }
 return B;
}
 
document.deepCss = function (who, css) {
 if (!who || !who.style) return '';
 var sty = css.replace(/\-([a-z])/g, function (a, b) {
 return b.toUpperCase();
 });
 if (who.currentStyle) {
 return who.style[sty] || who.currentStyle[sty] || '';
 }
 var dv = document.defaultView || window;
 return who.style[sty] ||
 dv.getComputedStyle(who, "").getPropertyValue(css) || '';
}
 
Array.prototype.indexOf = Array.prototype.indexOf ||
 function (what, index) {
 index = index || 0;
 var L = this.length;
 while (index < L) {
  if (this[index] === what) return index;
  ++index;
 }
 return -1;
 }

 var t = window.setTimeout("preLoad()", 100);
 function preLoad() {
 $("#loading div").animate({ width: step + "px" }, 50).text(step + "%");
 step += 1;
 if (step <= 100) {
  t = window.setTimeout("preLoad()", 100);
 } else {
  clearTimeout(t);
  $("#loading").fadeOut(1000);
  $("#preloadImg").fadeOut(1000);
  
  $(".main").show();
 }