Need help with regular expression

Question

I need a regular expression in javascript which does the following.

Those instances of a which are not the part of an HTML entity, should be replaced with w.

Ex:

abc should change to wbc

aabacaa should change to wwbwcww

&abcaa& should change to &wbcww&  

and so on.

I am using JavaScript.

Any help is appreciated.

Answer 1

a non-regex way, in your favourite programming language, split your string on "&a" (or &), replace the splitted items , then join back eg in Python

>>> s="&abcaa&"
>>> '&a'.join( [ i.replace("a","w") for i in  s.split("&a") ] )
'&wbcww&'

Answer 2

Try this:

"&abcaa&".replace(/&[^;]+;|a/g, function($0) {
    return $0 === "a" ? "w" : $0;
})

Answer 3

As a more general answer, when writing regular expressions, the first thing I do is to go to http://rubular.com and lay out a couple of test strings. I then write and re-work the regular expression until it does what I need.

Yes, I know Rubular is a Ruby regex site, but RegExp syntax is very similar, if not identical for most languages (I think Perl uses an extended syntax). I've successfully used Rubular to test Java RegExps.