javascript - regex for alphanumeric and special character

Question

Trying to build regex for string (company/organisation name) with below conditions:

no leading or trailing space
no double space in between
shouldn't allow only single character (alphanumeric or white listed)
can start with alphanumeric or white listed character
shouldn't allow any white listed character entered multiple times

regex for these: /(?! )([a-zA-Z0-9_\.\-#&])+([a-zA-Z0-9_\.\-#&\s])*(?<! )$/

console.log(/(?! )([a-zA-Z0-9_\.\-#&])+([a-zA-Z0-9_\.\-#&\s])*(?<! )$/.test('_')); // shouldn't allow

console.log(/(?! )([a-zA-Z0-9_\.\-#&])+([a-zA-Z0-9_\.\-#&\s])*(?<! )$/.test('a')); // shouldn't allow

console.log(/(?! )([a-zA-Z0-9_\.\-#&])+([a-zA-Z0-9_\.\-#&\s])*(?<! )$/.test('abc   abc')); // shouldn't allow

console.log(/(?! )([a-zA-Z0-9_\.\-#&])+([a-zA-Z0-9_\.\-#&\s])*(?<! )$/.test('_123')); // works fine

console.log(/(?! )([a-zA-Z0-9_\.\-#&])+([a-zA-Z0-9_\.\-#&\s])*(?<! )$/.test('# abc')); // works fine

console.log(/(?! )([a-zA-Z0-9_\.\-#&])+([a-zA-Z0-9_\.\-#&\s])*(?<! )$/.test('abc abc!')); // works fine

console.log(/(?! )([a-zA-Z0-9_\.\-#&])+([a-zA-Z0-9_\.\-#&\s])*(?<! )$/.test('abc abc# abc')); // works fine

current regex doesn't match all the criteria and couldn't figure out what's the problem with regex ?

@WiktorStribiżew this regex allows single character. /^[a-zA-Z0-9_.#&-]+(?: [a-zA-Z0-9_.#&-]+)*$/.test('#') this should return false but it returns true. — Valay
I see your expected match also has !, but your regex does not have it. I added ! to the character class in my answer. You may add more chars there, but mind - must stay at the end of the character class, right before ]. — Wiktor Stribiżew
@georg valid point. that shouldn't be allowed. updating requirements. thanks. — Valay

Wiktor Stribiżew Wiktor Stribiżew · Accepted Answer · 2018-12-12T14:31:42

You may use

/^(?=.{2})(?!(?:[^_.#&!-]*[_.#&!-]){2})[a-zA-Z0-9_.#&!-]+(?:\s[a-zA-Z0-9_.#&!-]+)*$/

Details

^ - start of string
(?=.{2}) - any 2 chars must be at the start
(?!(?:[^_.#&!-]*[_.#&!-]){2}) - no 2 occurrences of _.#&!- chars in the string
[a-zA-Z0-9_.#&-]+ - 1 or more allowed chars (other than whitespace)
(?:\s[a-zA-Z0-9_.#&!-]+)* - 0+ occurrences of
- \s - 1 whitespace
- [a-zA-Z0-9_.#&!-]+ - 1+ letters, digits and some symbols
$ - end of string.

JS demo

var rx = /^(?=.{2})(?!(?:[^_.#&!-]*[_.#&!-]){2})[a-zA-Z0-9_.#&!-]+(?:\s[a-zA-Z0-9_.#&!-]+)*$/;
console.log(rx.test('_')); // shouldn't allow
console.log(rx.test('a')); // shouldn't allow
console.log(rx.test('abc   abc')); // shouldn't allow
console.log(rx.test('_123')); // works fine
console.log(rx.test('# abc')); // works fine
console.log(rx.test('abc abc!')); // works fine
console.log(rx.test('abc abc# abc')); // works fine

javascript - regex for alphanumeric and special character

1 Answers