Question

Here is what i’ve got so far:

/(netscape)|(navigator)\/(\d+)(\.(\d+))?/.test(UserAgentString.toLowerCase()) ? ' netscape'+RegExp.$3+RegExp.$4 : ''

I’m trying to do several different things here.

(1). I want to match either netscape or navigator, and it must be followed by a single slash and one or more digits.

(2). It can optionally follow those digits with up to one of: one period and one or more digits.

The expression should evaluate to an empty string if (1) is not true.

The expression should return ' netscape8' if UserAgentString is Netscape/8 or Navigator/8.

The expression should return ' netscape8.4' if UserAgentString is Navigator/8.4.2.

The regex is not working. In particular (this is an edited down version for my testing, and it still doesn’t work):

// in Chrome this produces ["netscape", "netscape", undefined, undefined]
(/(netscape)|(navigator)\/(\d+)/.exec("Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US; rv:1.7.5) Gecko/20060912 Netscape/8.1.2".toLowerCase()))

Why does the 8 not get matched? Is it supposed to show up in the third entry or the fourth?

There are a couple things that I want to figure out if they are supported. Notice how I have 5 sets of capture paren groups. group #5 \d+ is contained within group #4: \.(\d+). Is it possible to retrieve the matched groups?

Also, what happens if I specify a group like this? /(\.\d+)*/ This matches any number of “dot-number” strings contatenated together (like in a version number). What’s RegExp.$1 supposed to match here?

Answer 1

Your “or” expression is not doing what you think.

Simplified, you’re doing this:

(a)|(b)cde

Which matches either a or bcde.

Put parentheses around your “or” expression: ((a)|(b))cde and that will match either acde or bcde.

I find http://regexpal.com/ to be a very useful tool for quickly checking my regex syntax.