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From: Ben Bacarisse <ben.usenet@bsb.me.uk>
Newsgroups: comp.lang.javascript
Subject: Re: Regular expression
Date: Sun, 15 Mar 2015 21:38:18 +0000
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"Tony Johansson" <johansson.andersson@telia.com> writes:

> Can somebody explain this regular expression
<snip> 
  replace(/([bcdfghjklmnpqrstvwxz])o\1/gi, '$1');

Match any one of bcdfghjklmnpqrstvwxz -- that's what the []s mean.
I.e. match a single non-vowel (taking y to be a vowel too).

Remember this matched letter -- that's what the ()s mean.

Match a single 'o'.

Match the non-vowel seen before -- that's what the \1 means.

Do this globally (i.e. repeat for very match) -- that's the 'g' -- and
ignoring case -- that's the 'i'.

For every such match, replace it with the single-letter non-vowel.  '$1'
in a replacement string means the first captured match.

-- 
Ben.