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Regex to match instances of X unless they're within comments

I have this regex that matches an 'if' statement if it follows a comment:
(?:(\/\*[\w\s\']*)|(\/\/[\w\s\']*))if
What I need is to find all instances of 'if' as long as they don't match the regex above, so if the 'if' statement is within comments ignore it, otherwise match it. Is this possible with Regex alone? This feels like its very close.

How about first cleaning the code from comments using REGEX and then make a second run on the clean code?
I did it in SQL using REGEXP_REPLACE with a PCRE dialect but I'm sure you'll get the hang of it
SQL/Regex Challenge/Puzzle: How to remove comments from SQL code (by using SQL query)?
P.s.
You might also want to remove string using the same concept.

Best practice for specifying number of new lines in regex

Since long I am using this for specifying new line and it works fine.
(?:.*[\r\n]+){n,m}
Is this the best practice for doing this?

It's better to use (?:.*\r?\n){n,m} since [\r\n]+ in your regex should match one or more newline chars greedily. So it won't do the exact work you want.

Best way to match and catch doubly-entified character entities/references?

I'm talking about stuff like & which will then render to: & when it actually should render to &. In this I asked how to match entities, but it seems that isn't really possible or realistic with regexes. What then is the best way to match double entities?
EDIT: Is this a good way to do it? .replace(/&(?=#?x?[0-9a-z]+);/i, '&');
(I'm using javascript)

I'd go with
pattern &([a-zA-Z0-9]+?;)\1
replacement &$1
to replace just double amps, or:
pattern &([#a-zA-Z0-9]+?;)
EDIT:
your pattern
/&(?=#?x?[0-9a-z]+);/i
looks also good to me.
Note: none of these is something you can trust

Possibly:
&[a-zA-Z]+;
Though not fool proof.

Normalize your data first. Use whatever you know about encoding to decode them back to form where character/piece of data have only one possible encoding. After that match this normalized data with normalized pattern.

How To Create This RegExp

I am looking to find this in a string: XXXX-XXX-XXX Where the X is any number.
I need to find this in a string using JavaScript so bonus points to those who can provide me the JavaScript too. I tried to create a regex and came out with this: ^[0-9]{4}\-[0-9]{3}\-[0-9]{3}$
Also, I would love to know of any cheat sheets or programs you guys use to create your regular expressions.

i suppose this is what you want:
\d{4}-\d{3}-\d{3}
in doubt? Google for "RegEx Testers"

With your attempt:
^[0-9]{4}\-[0-9]{3}\-[0-9]{3}$
Since the - is not a metacharacter, there is no need to escape it -- thus you are looking for explicit backslash characters.
Also, you've anchored the match at the beginning and end of the string -- this will match only strings that consist only of your number. (Well, assuming the rest were correct.)
I know most people like the {3} style of counting, but when the thing being matched is a single digit, I find this more legible:
\d\d\d\d-\d\d\d-\d\d\d
Obviously if you wanted to extend this to matching hexadecimal digits, extending this one would be horrible, but I think this is far more legible than alternatives:
\d{4}-\d{3}-\d{3}
[[:digit:]]{4}-[[:digit:]]{3}-[[:digit:]]{3}
[0-9]{4}-[0-9]{3}-[0-9]{3}
Go with whatever is easiest for you to read.
I tend to use the perlre(1) manpage as my main reference, knowing full well that it is far more featureful than many regexp engines. I'm prepared to handle the differences considering how conveniently available the perlre manpage is on most systems.

var result = (/\d{4}\-\d{3}\-\d{3}/).exec(myString);

Wipe a string but keep its middle part

With a string like "HorsieDoggieBirdie", is there a non-capturing regex replace that would kill "Horsie" and "Birdie", yet keep "Doggie" intact? I can only think of a capturing solution:
s/(Horsie)(Doggie)(Birdie)/$2/g
Is there a non-capturing solution like:
s/Horsie##Doggie##Birdie//g
where ## is some combination of regex codes? The specific problem is in JavaScript (innerHTML.replace) but I'll take Perl suggestions, too.

You don't have to capture the Horsie or the Birdie.
s/Horsie(Doggie)Birdie/$1/g;
A similar thing should work for Javascript as well. This is probably as efficient as it gets, and at least as fast as using look-around assertions; although you should benchmark it if you want to know for sure. (The results, of course, will depend on the horsies, doggies and birdies in question.)
Mandatory disclaimer: you should know what happens when you use regular expressions with HTML...

You can use Look-Around Assertions:
s/(?:Horsie(?=Doggie))|(?:(?<=Doggie)Birdie)//g;