javascript

Chapter 9: Client Detection
The Gecko version number appears between ” rv: ” and a closing parenthesis, so to extract the version
number, the regular expression looks for all characters that are not a closing parenthesis. The regular
expression also looks for the string ” Gecko/ ” followed by eight numbers. If the pattern matches, then
the version number is extracted and stored in the appropriate properties. Gecko version numbers are
related to Firefox versions as detailed in the following table.
Firefox Version
Minimum Gecko Version
1.0 1.7.5
1.5 1.8
2.0 1.8.1
3.0 1.9
As with Safari and WebKit, matches between Firefox and Gecko version numbers are not exact.
IE is the last rendering engine to detect. The version number is found following ” MSIE ” and before a
semicolon, so the regular expression is fairly simple, as you can see in the following example:
var ua = navigator.userAgent;
if (window.opera){
engine.ver = window.opera.version();
engine.opera = parseFloat(client.ver);
} else if (/AppleWebKit\/(\S+)/.test(ua)){
engine.ver = RegExp[“$1”];
engine.webkit = parseFloat(client.ver);
} else if (/KHTML\/(\S+)/.test(ua)){
engine.ver = RegExp[“$1”];
engine.khtml = parseFloat(client.ver);
} else if (/rv:([^\)]+)\) Gecko\/\d{8}/.test(ua)){
engine.ver = RegExp[“$1”];
engine.gecko = parseFloat(client.ver);
} else if (/MSIE ([^;]+)/.test(ua)){
engine.ver = RegExp[“$1”];
engine.ie = parseFloat(client.ver);
}
The last part of this rendering engine ’ s detection script uses a negation class in the regular expression to
get all characters that aren ’ t a semicolon. Even though IE typically keeps version numbers as standard
floating - point values, that won ’ t necessarily always be so. The negation class [^;] is used to allow for
multiple decimal points and possibly letters.
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