Detect Search Crawlers via JavaScript

I am wondering how would I go abouts in detecting search crawlers? The reason I ask is because I want to suppress certain JavaScript calls if the user agent is a bot.

I have found an example of how to to detect a certain browser, but am unable to find examples of how to detect a search crawler:

/MSIE (\d+\.\d+);/.test(navigator.userAgent); //test for MSIE x.x

Example of search crawlers I want to block:

Google Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html) Googlebot/2.1 (+http://www.googlebot.com/bot.html) Googlebot/2.1 (+http://www.google.com/bot.html) Baidu Baiduspider+(+http://www.baidu.com/search/spider_jp.html) Baiduspider+(+http://www.baidu.com/search/spider.htm) BaiDuSpider