javascript regex validation issue

Question

I am writing a javascript regex for the following:

must have at least one digit
must have at least one capital letter
must be between 8-15 characters

I have tried it like this:

function isStrongPassword(strInput) {
    //works well except A1aaaaaa
    var regex = /^(?=.*\d)(^[A-Za-z0-9])(?=.*[A-Z]).{7,14}$/; 
    return regex.test(strInput);
}

This is working properly, except the fact it is not matching with A1aaaaaa, which is a valid input.

Any help is appreciated.

Felix Kling · Accepted Answer · 2013-02-22 09:48:47Z

1

Your expression fails because of (?=.*[A-Z]). None of the characters following the first one is upper case.

It seems this expression should suffice:

^(?=[^\d]*\d)(?=[^A-Z]*[A-Z]).{8,15}$

Note that switching .* to [^...]* has nothing to do with your problem, but it avoids backtracking. Alternatively you could use lazy matching: .*?.

answered Feb 22, 2013 at 9:48

Felix Kling

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2 Comments

tusar Over a year ago

sir, the regex you have given works very well. I didnt get why in my case I had to give 7,14 but in your regex you did the length checking with 8,15 ?

Felix Kling Over a year ago

Because in your expression, (^[A-Za-z0-9]) already matched and consumed a character, so there would be only 7 to 14 let to match. In my expression, there are only lookaheads, which don't consume any characters, so the . has to match 8 to 15 times.

Billy Moon · Accepted Answer · 2013-02-22 09:51:45Z

1

Your regex was breaking because of the (^[A-Za-z0-9]) part, which would mean that after a digit, there must be a letter or digit, and then a capital letter. This should work

/^(?=.*\d)(?=.*[A-Z]).{8,15}$/;

Which breaks down like this...

/              
^              # start match
(?=.*\d)       # is there a digit up ahead (maybe after zero or more anythings)
(?=.*[A-Z])    # is there a capital up ahead (maybe after zero or more anythings)
.{8,15}        # 8 to 15 anythings
$              # end match
/

answered Feb 22, 2013 at 9:51

Billy Moon

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4 Comments

tusar Over a year ago

I have not tried yet your answer. But my regex does match with 1Aaaaaaa , aaaaaaA1, 111Aaaa etc... I think it is not the reason.

Billy Moon Over a year ago

The reason is, that it specifies a letter or number to start the regex, and then afterwards, to have a capital letter. So it does not match your test, which only has a capital at the beginning, and not after that.

tusar Over a year ago

oh yes, now I get your point. thanks so much for the explanation. regex is my weak side :)

Billy Moon Over a year ago

regex is a dark art, usually problematic, always under-commented, occasionally indispensable.

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