How to make a proper Javascript regex?

Question

I would like to make regular expression so it matches only value as bellow, but I want to make it so you have to have at least one (i know it works with the "+" symbol) a-z letter, but I don't know where to put the "+" to make it work correctly. Any help on this?

.match(/^[0-9a-z]{3,10}$/i)

Edit: It should match for string like "12a", but it shouldn't match for "123" cause it has to have at least one a-z in it.

if( ! ($Username.match(/^[0-9a-z]{3,10}$/i) && $Username.match(/[a-z]/i)) ) {
    return false;
}

Edit: Thanks to Felix now the example code above works perfect.

It always helps with regex questions if you post a few strings that should match and a 1 or more should not match. — Kyle Wild
– Kyle Wild, Commented Jan 21, 2011 at 20:07
Some would deem “proper Javascript regex” to be oxymoronic. :) — tchrist
– tchrist, Commented Jan 21, 2011 at 20:20
It has to be $Username.match(/[a-z]/i). a-z must be in a character class, otherwise it matches a-z literally. — Felix Kling
– Felix Kling, Commented Jan 21, 2011 at 20:27

Felix Kling · Accepted Answer · 2011-01-21 20:29:51Z

3

Assuming you mean:

Between 3 and 10 characters (inclusive)
All letters or numbers
At least one letter in any position

Then the simplest way to achieve this would be:

foo.match(/^[0-9a-z]{3,10}$/i) && foo.match(/[a-z]/i);

edited Jan 21, 2011 at 20:29

Felix Kling

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answered Jan 21, 2011 at 20:05

Quentin

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5 Comments

Quentin Over a year ago

@subtenante — thanks for the catch, fixed. This is what comes of too much exposure to jQuery ;)

Rihards Over a year ago

Wondering if doing to reg exp matches is more efficient than doing one, but a little bit complicated?

Quentin Over a year ago

@Richards — assuming that such a regex exists (nobody has suggested one that meets the outlined conditions so far), then simple beats efficient until there is a real performance problem. "premature optimization is the root of all evil" — Donald Knuth

glmxndr Over a year ago

There is none, don't look for it farther. What Richards describes is neither right-linear nor left-linear. Ergo : it's not regular.

Rihards Over a year ago

@daviddorward, actually I'm having trouble to get your example working.. Added code to first post.

glmxndr · Accepted Answer · 2011-02-02 11:00:39Z

2

You can't do it in a single step. The expression you talk about is not regular. You have to make it in several steps. Just match with your current expression and combine to the match with a /[a-z]/ expression.

edited Feb 2, 2011 at 11:00

answered Jan 21, 2011 at 20:06

glmxndr

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Comments

Kyle Wild · Accepted Answer · 2011-01-21 20:23:39Z

0

I believe this will do the filtering, although you'll have to check the character count separately:

^[0-9a-z]*[a-z]+[0-9a-z]*$

edited Jan 21, 2011 at 20:23

answered Jan 21, 2011 at 20:04

Kyle Wild

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5 Comments

Quentin Over a year ago

That regex doesn't even compile.

Felix Kling Over a year ago

This does not enforce one letter.

Kyle Wild Over a year ago

Now that the OP has clarified the post, I've updated my answer to (i think) solve it

Felix Kling Over a year ago

This does not enforce 3 to 10 characters ;)

Kyle Wild Over a year ago

Well to my credit -- While one might infer that from the OP's regex attempt, neither his copy nor his examples specified it :)

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