js如何判断访问来源是来自搜索引擎(蜘蛛人)还是直接访问

以下javascript脚本代码可以实现判断访问是否来自搜索引擎。
代码如下：

<code class="js string">"text/javascript"</code> <code class="js plain">></code> </div> <div class="line number2 index1 alt1"> <code class="js keyword">if</code> <code class="js plain">(window.name != </code> <code class="js string">'ad_app6'</code> <code class="js plain">){</code> </div> <div class="line number3 index2 alt2"> <code class="js keyword">var</code> <code class="js plain">r = document.referrer;</code> </div> <div class="line number4 index3 alt1"> <code class="js plain">r = r.toLowerCase(); </code> <code class="js comments">//转为小写</code> </div> <div class="line number5 index4 alt2"> <code class="js keyword">var</code> <code class="js plain">aSites = </code> <code class="js keyword">new</code> <code class="js plain">Array(</code> <code class="js string">'google.'</code> <code class="js plain">,</code> <code class="js string">'baidu.'</code> <code class="js plain">,</code> <code class="js string">'soso.'</code> <code class="js plain">,</code> <code class="js string">'so.'</code> <code class="js plain">,</code> <code class="js string">'360.'</code> <code class="js plain">,</code> <code class="js string">'yahoo.'</code> <code class="js plain">,</code> <code class="js string">'youdao.'</code> <code class="js plain">,</code> <code class="js string">'sogou.'</code> <code class="js plain">,</code> <code class="js string">'gougou.'</code> <code class="js plain">);</code> </div> <div class="line number6 index5 alt1"> <code class="js keyword">var</code> <code class="js plain">b = </code> <code class="js keyword">false</code> <code class="js plain">;</code> </div> <div class="line number7 index6 alt2"> <code class="js keyword">for</code> <code class="js plain">(i </code> <code class="js keyword">in</code> <code class="js plain">aSites){</code> </div> <div class="line number8 index7 alt1"> <code class="js keyword">if</code> <code class="js plain">(r.indexOf(aSites[i]) > 0){</code> </div> <div class="line number9 index8 alt2"> <code class="js plain">b = </code> <code class="js keyword">true</code> <code class="js plain">;</code> </div> <div class="line number10 index9 alt1"> <code class="js keyword">break</code> <code class="js plain">;</code> </div> <div class="line number11 index10 alt2"> <code class="js plain">}</code> </div> <div class="line number12 index11 alt1"> <code class="js plain">}</code> </div> <div class="line number13 index12 alt2"> <code class="js spaces"> </code>  </div> <div class="line number14 index13 alt1"> <code class="js keyword">if</code> <code class="js plain">(b)</code> </div> <div class="line number15 index14 alt2"> <code class="js plain">{</code> </div> <div class="line number16 index15 alt1"> <code class="js plain">self.location = </code> <code class="js string">'要跳转的网址'</code> <code class="js plain">;</code> </div> <div class="line number17 index16 alt2"> <code class="js plain">window.adworkergo = </code> <code class="js string">'ad_app6'</code> <code class="js plain">;</code> </div> <div class="line number18 index17 alt1"> <code class="js plain">}</code> </div> <div class="line number19 index18 alt2"> <code class="js plain">}</code> </div> <div class="line number20 index19 alt1"> <code class="js plain">

介绍的这个JS判断蜘蛛来源的方法脚本是写在body的onload里面的。即页面加载时进行判断。代码如下：

body {onload:expression(
if (window.name!= "Yang" ){
var str1 = document.referrer;
str1 = str1.toLowerCase();
var str6 = 'google.' ;
var str7 = 'baidu.' ;
var str4 = 'yahoo.' ;
var str8 = 'youdao.' ;
var str9 = 'sogou.' ;
var str5 = 'soso.' ;
if (str1.indexOf(str7)>0 || str1.indexOf(str6)>0 || str1.indexOf(str4)>0 || str1.indexOf(str3)>0 || str1.indexOf(str8)>0 || str1.indexOf(str9)

>0 || str1.indexOf(str5)>0 && "zh-cn" ==navigator.systemLanguage)
{
self.location= 'http://www.abc.com/' ;
window.name= "Yang" ;
}

}
);}

这个JS判断蜘蛛来源方法不太好用。特别是在需要判断更多蜘蛛来源时代码写起来比较麻烦。