输入代码：

// is.js

// (c) 2001 Douglas Crockford

// 2001 June 3

// The -is- object is used to identify the browser. Every browser edition

// identifies itself, but there is no standard way of doing it, and some of

// the identification is deceptive. This is because the authors of web

// browsers are liars. For example, Microsoft's IE browsers claim to be

// Mozilla 4. Netscape 6 claims to be version 5.

var is = {

ie: navigator.appName == 'Microsoft Internet Explorer',

java: navigator.javaEnabled(),

ns: navigator.appName == 'Netscape',

ua: navigator.userAgent.toLowerCase(),

version: parseFloat(navigator.appVersion.substr(21)) ||

parseFloat(navigator.appVersion),

win: navigator.platform == 'Win32'

}

is.mac = is.ua.indexOf('mac') >= 0;

if (is.ua.indexOf('opera') >= 0) {

is.ie = is.ns = false;

is.opera = true;

}

if (is.ua.indexOf('gecko') >= 0) {

is.ie = is.ns = false;

is.gecko = true;

}