图片预加载（代理模式）

imagePreloader.js

var myImage = (function (){
  var imgNode = document.createElement('img');
  document.body.appendChild(imgNode);
  return {
    setSrc: function(src){
      imgNode.src = src;
    }
  }
})();

var proxyImage = (function (){
  var img = new Image;
  img.onload = function (src){
    myImage.setSrc(src);
  }
  return {
    setSrc: function (src){
      myImage.setSrc('file:// /C:/img/preLoading.gif');
      img.src = srac;
    }
  }
})();

proxyImage.setSrc('http://dd.s.dd.s/real.png');