Question 231570 in Javascript Question posted in
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Javascript – regex addition of character or number at the beginning and end of string

i have the following conditions i’m trying to meet with a regex (for a username validation):

  • It must be between 6 and 30 characters long.
  • It cannot have two consecutive periods, hyphens,underscores, or @ symbols.
  • It must start and end with a letter or number.

i have the following which seems to work for the first two conditions, what would i add for the 3rd?

^(?=.{6,30}$)(?![.@-])(?!.*[_.@-]{2})^[a-zA-Z0-9._@-]{2,}[a-zA-Z0-9]$

examples of valid strings:

[email protected]
1test-user
[email protected]
123456
asdfghjklpoiuytrewqasdfghjklpo
derghg$56

invalid

[email protected]
[email protected]!
test..user
test_.
Tags:

2

Answers


  1. 0

    You can make a negative match, looking for invalid patterns. That makes it easy just combine with | anything you want.

    The only problem I don’t understand

    It cannot have two consecutive periods, hyphens,underscores, or @ symbols.

    whether it’s about the same symbol or any from the list.

    Anyway I hope you got the idea:

    /*
It must be between 6 and 30 characters long.
It cannot have two consecutive periods, hyphens,underscores, or @ symbols.
It must start and end with a letter or number.
*/
const valid = `
[email protected]
1test-user
[email protected]
12345
asdfghjklpoiuytrewqasdfghjklpo
`;

const invalid = `
user%name
[email protected]
[email protected]!
test..user
test_.
`;

// 12345 - seems invalid since less than 6 chars

const names = ['ok_user@name', '[email protected]', 'asdf', 'asdfasdfasdfasdfasdfasdfasdfasdfasdfasdfasd', '_asdfs', '2asdf__']
names.unshift(...valid.match(/S+/g));
names.unshift(...invalid.match(/S+/g));

names.forEach(str => 
  console.log(str, 'is valid:', !/^.{0,5}$|^.{31,}$|[-_.@]{2}|^[^a-z0-9]|[^[^a-z0-9]$|[^-w_.@]/.test(str))
);
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  2. 0

    1. Studying your regex, you seem to have a 4th condition: only allowed characters are alphanumerics,hyphens,underscores, or @ symbols.

    2. So, why don’t you combine what is at the start with what is at the end? First do your duplicate lookahead check (?!.*[_.@-]{2}) and then recognize that a string of 6-30 with alphanumerics at each end is the same as a 4-28 string sandwiched between alphanumerics [A-Z0-9][w.@-]{4,28}[A-Z0-9]. Put them together with:

    ^(?!.*[_.@-]{2})[A-Z0-9][w.@-]{4,28}[A-Z0-9]$

    If you assert the case insensitive flag (i), doesn’t that take care of it?

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