function addCookie(objName,objValue,objHours) {
  var str = objName + "=" + escape(objValue);
  if(objHours > 0){
    var date = new Date();
    var ms = objHours*3600*1000;
    date.setTime(date.getTime() + ms);
    str += "; expires=" + date.toGMTString();
  }
  document.cookie = str;
}
function getCookie(objName) {
  var arrStr = document.cookie.split("; ");
  for(var i = 0;i < arrStr.length;i ++){
    var temp = arrStr[i].split("=");
    if(temp[0] == objName) return unescape(temp[1]);
  }
}
function delCookie(name) {
  var date = new Date();
  date.setTime(date.getTime() - 10000);
  document.cookie = name + "=a; expires=" + date.toGMTString();
}

//预加载图片
<script type="text/javascript">
  var imgname=new Array();
  var img = new Array();
  //要预先加载图片,如果只有一张就可以不用数组，
  imgname[0]="images/200709/1190103232193726715.jpg";  
  imgname[1]="images/200709/1190103232486901779.jpg";  
  //预读图片
  for (i=0;i<=imgname.length-1;i++)
  {
      img[i] = new Image();
      img[i].src = imgname[i];
  }
</script>