This string is returned to a web server in the USER-AGENT: header of an HTTP request. This is often logged and processed to analyze the distribution of browser types across the user base for a site.

The userAgent string contains much useful information and generally includes everything the appVersion and appName properties would have told you as well.

Here are some typical values:

• Mozilla/4.7 (Macintosh; I; PPC)

• Mozilla/4.0 (compatible; MSIE 4.5; Mac_PowerPC)

• Mozilla/4.0 (compatible; MSIE 5.0; Mac_PowerPC)

Warnings:

• Beware that some customized browsers will encode a variety of strange textual values into their userAgent property.

• While this will only affect the user of the browser when they run your script, the nature of the userAgent string may cause your script to fail.

• The following unusual values have been encountered in userAgent strings:

- Null characters

- Control characters

- URL strings

- HTML

- C-Code

- JavaScript

- GIF image data

- Very large text blocks

• These appear to be intended to cause server difficulties and possibly malfunctions in logging analysis systems. They may, as a side effect cause your script to crash and burn too.

Example code:

   // A function to normalize the user agent string

   function getBrowserType()

   {

   var myUserAgent;

   var myMajor;

   myUserAgent   = navigator.userAgent.toLowerCase();

   myMajor       = parseInt(navigator.appVersion);

   if( (myUserAgent.indexOf('mozilla')    != -1) &&

   (myUserAgent.indexOf('spoofer')    == -1) &&

   (myUserAgent.indexOf('compatible') == -1) &&

   (myUserAgent.indexOf('opera')      == -1) &&

   (myUserAgent.indexOf('webtv')      == -1)

   )

   {

   if (myMajor > 4)

   {

   return "nav6";

   }

   if (myMajor > 3)

   {

   return "nav4";

   }

   return "nav";

   }

   if (myUserAgent.indexOf("msie") != -1)

   {

   if (myMajor > 4)

   {

   return "ie5";

   }

   if (myMajor > 3)

   {

   return "ie4";

   }

   return "ie";

   }

   return "other";

   }

Property attributes:

ReadOnly