方法如下：
1 var show_navigator = navigator.userAgent.toLowerCase();
2 document.write(show_navigator); IE6:
mozilla/4.0 (compatible; msie 6.0; windows nt 5.1; .net clr 2.0.50727)
IE7:
mozilla/4.0 (compatible; msie 7.0; windows nt 5.1; .net clr 2.0.50727)
IE8:
mozilla/4.0 (compatible; msie 8.0; windows nt 5.1; trident/4.0; .net clr 2.0.50727)
Chrome:
mozilla/5.0 (windows nt 5.1) applewebkit/535.7 (khtml, like gecko) chrome/16.0.912.77 safari/535.7
Firefox:
mozilla/5.0 (windows nt 5.1; rv:10.0) gecko/20100101 firefox/10.0
Opera:
opera/9.80 (windows nt 5.1; u; edition ibis; zh-cn) presto/2.10.229 version/11.61
Safari:
mozilla/5.0 (windows nt 5.1) applewebkit/534.52.7 (khtml, like gecko) version/5.1.2 safari/534.52.7