从网易扒过来的js调用广告显示文件(随机几率)

从网易撬过来的js调用广告显示文件
只有下面短短几行代码可以随机显示flash和gif广告，还不错

function column02(imgsource,url,chance,type) {
this.imgsource = imgsource;
this.url = url;
this.chance = chance;
this.type = type;
}
function dispcolumn02() {
with (this)
switch (type){
case "img":
document.write("<a href=" + url + " target=_blank><img src=" + imgsource + " width=480 height=250 border=0></a>");
break;
case "html":
document.write("<iframe width=480 height=250 marginwidth=0 marginheight=0 hspace=0 vspace=0 frameborder=0 scrolling=no bordercolor=#000000 src="+ imgsource + "></iframe>");
break;
case "flash":
document.write("<embed src="+imgsource+" quality=high width=480 height=250 type=application/x-shockwave-flash pluginspage=http://www.macromedia.com/shockwave/download/index.cgi?p1_prod_version=shockwaveflash></embed>");
break;
default:
document.write("");
}
}
column02.prototype.dispcolumn02 = dispcolumn02;
columns02 = new array();
// flash , html , img 代表三种不同的广告模式
// 200 之类的数目是设置出现的机率
columns02[0] = new column02("http://smsimg.163.com/honey/honey_ad.swf","",200,"flash");//主广告
columns02[1] = new column02("http://smsimg.163.com/honey/honey_photo.swf","",800,"flash"); //上传图片免月租
columns02[2] = new column02("http://smsimg.163.com/honey/honey_gold.swf","",800,"flash"); //登陆送金币
//columns02[] = new column02("f","",100,"");// （20030422～20030722）
sum_of_all_chances = 0;
for (i = 0; i < columns02.length; i++) {
sum_of_all_chances += columns02[i].chance;
}
function randomcolumn02() {
chance_limit = 0;
randomly_selected_chance = math.round((sum_of_all_chances - 1) * math.random()) + 1;
for (i = 0; i < columns02.length; i++) {
chance_limit += columns02[i].chance;
if (randomly_selected_chance <= chance_limit) {
columns02[i].dispcolumn02();
break;
}
}
}
this_column02 = randomcolumn02();

测试代码，chance越大显示的几率越大

[ctrl+a 全选 注:引入外部js需再刷新一下页面才能执行]