Non-capturing groups in Javascript regex

Question

I am matching a string in Javascript against the following regex:

(?:new\s)(.*)(?:[:])

The string I use the function on is "new Tag:var;" What it suppod to return is only "Tag" but instead it returns an array containing "new Tag:" and the desired result as well.

I found out that I might need to use a lookbehind instead but since it is not supported in Javascript I am a bit lost.

Thank you in advance!

zmo · Accepted Answer · 2014-01-30 13:29:36Z

1

Well, I don't really get why you make such a complicated regexp for what you want to extract:

(?:new\\s)(.*)(?:[:])

whereas it can be solved using the following:

s = "new Tag:";
var out = s.replace(/new\s([^:]*):.*;/, "$1")

where you got only one capturing group which is the one you're looking for.

answered Jan 30, 2014 at 13:29

zmo

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2 Comments

zmo Over a year ago

and as @anubhava states, .* is "greedy" and not a good idea, because if you got two or more columns in your string, it may match only the last one.

MCB Over a year ago

That overly greedy operator was driving me crazy.

anubhava · Accepted Answer · 2014-01-30 13:28:00Z

1

\\s (double escaping) is only needed for creating RegExp instance.
Also your regex is using greedy pattern in .* which may be matching more than desired.

Make it non-greedy:

(?:new\s)(.*?)(?:[:])

OR better use negation:

(?:new\s)([^:]*)(?:[:])

answered Jan 30, 2014 at 13:28

anubhava

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1 Comment

David Simon Over a year ago

My bad, the extra '\' was for escaping. Otherwise, string.match() still returns an array containing two entries

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