判断浏览器的类型

用js判断浏览器的类型有很多方法，典型的是根据navigator.userAgent或浏览器的不同js特征等。

1. 根据navigator.userAgent判断

在页面中加入：

<script type="text/javascript">
  alert(navigator.userAgent);
  alert(navigator.product);
</script>

结果示例：
IE9
userAgent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; InfoPath.2; MS-RTC LM 8; .NET4.0C; .NET4.0E)
product: undefined

Firefox 13.0.1
userAgent: Mozilla/5.0 (Windows NT 6.1; rv:13.0) Gecko/20100101 Firefox/13.0.1
product: Gecko

Chrome 20.0.1132.47 m
userAgent: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/536.11 (KHTML, like Gecko) Chrome/20.0.1132.47 Safari/536.11
product: Gecko

Safari 5.1.1
userAgent: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/534.51.22 (KHTML, like Gecko) Version/5.1.1 Safari/534.51.22
product: Gecko

代码示例：

var isOpera = (navigator.userAgent.indexOf("Opera") != -1);
var isMSIE = (navigator.userAgent.indexOf("MSIE") != -1) && (!isOpera);
var isGecko = (navigator.userAgent.indexOf("Gecko") != -1) && (!isOpera);
var isChrome = (navigator.userAgent.indexOf("Chrome") != -1);
var isSafari = (navigator.userAgent.indexOf("Safari") != -1) && (!isChrome);

2. 根据浏览器特征

// IE
document.all
window.event
window.attachEvent

// Firefox
window.addEventListener