Develop Reference

JavaScript regex with below rules

Need to create a regex for a string with below criteria
Allowable characters:
uppercase A to Z A-Z
lowercase a to z a-z
hyphen `
apostrophe '
single quote '
space
full stop .
numerals 0 to 9 0-9
Validations:
Must start with an alphabetic character a-zA-Z or apostrophe
Cannot have consecutive non-alpha characters except for a full stop followed by a space.
The regex I have from the previous question in this forum. Business came back and want to allow string starting with apostrophe along with [a-zA-Z]. This break some previous validations.
eg: a1rte is valid
'tyer4 is valid
'4rt is invalid
^(?!.*[0-9'`\.\s-]{2})[a-zA-Z][a-zA-Z0-9-`'.\s]+$
Please advise.

You might use
^(?=[a-zA-Z0-9`'. -]+$)(?!.*[0-9'` -]{2})[a-zA-Z'][^\r\n.]*(?:\.[ a-z][^\r\n.]*)*$
Explanation
^ Start of string
(?=[a-zA-Z0-9`'. -]+$) Assert only allowed characters
(?!.*[0-9'` -]{2}) Assert not 2 consecutive listed characters
[a-zA-Z'] Match either a char a-zA-Z or apostrophe
[^\r\n.]* Optionally match any char except a newline or a dot
(?:\.[ a-z][^\r\n.]*)* Optionally repeat matching a dot only followed by a space or char a-z
$ End of string
Regex demo

Regex for validating statement descriptor for credit card statements

I'm trying to validate a string entered by the user to be used as the statement description on the credit card statement to describe the purchase.
The requirements are:
Must be between 5 and 22 characters long
Must contain at least one letter (case doesn't matter)
Cannot contain these characters: < > \ ' "
Only ASCII characters allowed
Here's what I've got so far, which is kind of working:
/^(?=.*?[a-zA-Z])[a-zA-Z0-9]{5,22}$/gm
...in that it correctly checks the length for 5-22 characters long and checks for at least one letter. However, it disallows all special characters and diacritics instead of just the few that aren't allowed. How do I modify it to allow the other allowed characters?

You could use a positive lookahead to assert a character and a negative lookahead to assert not to match any character listed in the character class.
For Javascript you can use the case insensitive flag /i and use [a-z].
Edit: As Wiktor Stribiżew points out, to match only ASCII characters you could use [\x00-\x7F] instead of using a dot.
^(?=.*[a-z])(?!.*[<>\\'"])[\x00-\x7F]{5,22}$
^ Start of string
(?=.*[a-z]) Positive lookahead to check if there is a ASCII letter
(?!.*[<>\\'"]) Negative lookahead to check that there is not any of the chars in the character class
[\x00-\x7F]{5,22} Match any ASCII character 5 - 22 times
$ End of the string
For example:
const regex = /^(?=.*[a-z])(?!.*[<>\\'"])[\x00-\x7F]{5,22}$/gmi;
See the regex demo

You may use
/^(?=[^a-z]*[a-z])(?:(?![<>\\'"])[\x00-\x7F]){5,22}$/i
/^(?=[^a-z]*[a-z])(?![^<>\\'"]*[<>\\'"])[\x00-\x7F]{5,22}$/i
If you mean printable ASCII chars are allowed use
/^(?=[^a-z]*[a-z])(?:(?![<>\\'"])[ -~]){5,22}$/i
/^(?=[^a-z]*[a-z])(?![^<>\\'"]*[<>\\'"])[ -~]{5,22}$/i
Details
^ - start of string
(?=[^a-z]*[a-z]) - there must be at least 1 ASCII letter in the string
(?:(?![<>\\'"])[ -~]){5,22} - five to twenty-two occurrences of any printable ASCII char other than <, >, \, ' and " (if [\x00-\x7F] is used, any ASCII char other than the chars in the negated character class)
(?![^<>\\'"]*[<>\\'"]) - no <, >, \, ' and " allowed in the string
$ - end of string.

Angularjs regex validation

I want to make an Angularjs regex validation that allow all alphabets, numbers, space and following special characters ! ' " & - ( )

You may use
ng-pattern="/^[a-zA-Z0-9\s!'\x22&()-]*$/"
Details
^ - start of string
[a-zA-Z0-9\s!'\x22&()-]* - 0 or more:
a-zA-Z - ASCII letters
0-9 - ASCII digits
\s - whitespaces
!'\x22&()- - !, ', " (\x22 matches "), &, (, ) or - (the hyphen must be at the end/start of the character class or escaped to denote a literal -)
$ - end of string.

regular expression to match name with only one spaces

I have a string condition in js where i have to check whether name entered in text box contains with one space only.
pattern: name.status === 'full_name' ? /^[a-zA-Z.+-.']+\s+[a-zA-Z.+-. ']+$/ : /^[a-zA-Z.+-. ']+$/
But the above regex matches names ending with 2 spaces also.
I need to match it such that the entered name should accept only one space for a name string. So the name will have only one space in between or at the end.

Two observations: 1) \s+ in your pattern matches 1 or more whitespaces, and 2) [+-.] matches 4 chars: +, ,, - and ., it is thus best to put the hyphen at the end of the character class.
You may use
/^[a-zA-Z.+'-]+(?:\s[a-zA-Z.+'-]+)*\s?$/
See the regex demo
Details
^ - start of string
[a-zA-Z.+'-]+ - 1 or more letters, ., +, ' or -
(?:\s[a-zA-Z.+'-]+)* - zero or more sequences of:
\s - a single whitespace
[a-zA-Z.+'-]+ - 1 or more letters, ., +, ' or - chars
\s? - an optional whitespace
$ - end of string.
Note: if the "names" cannot contain . and +, just remove these symbols from your character classes.

/^\S+\s\S+$/
try this
Some explanations:
^ - start of string
\s - single whitespace
\S - everything except whitespace
"+"- quantifier "one or more"
$ - end of string

you could also use word boundaries...
function isFullName(s) {
return /^\b\w+\b \b\w+\b$/.test(s);
}
['Giuseppe', 'Mandato', 'Giuseppe Mandato']
.forEach(item => console.log(`isFullName ${item} ? ${isFullName(item)}`))

validation format of javascript

I found these javascript validation codes:
<script type="text/javascript">
function validasi_input(form){
pola_username=/^[a-zA-Z0-9\_\-]{6,100}$/;
if (!pola_username.test(form.username.value)){
alert ('Username minimal 6 karakter dan hanya boleh Huruf atau Angka!');
form.username.focus();
return false;
}
return (true);
}
</script>
I want to ask about this part:
pola_username=/^[a-zA-Z0-9\_\-]{6,100}$/;
does anyone can tell me how to understand this kind of format? is it format for letter, or number, or characters?

/^[a-zA-Z0-9\_\-]{6,100}$/;
In english this means: that a string can have any letter either uppercase or lowercase, numbers, underscores, and hyphens. A minimum length of 6 characters, and a maximum length of 100.
Further details:
The string must start with either a letter, number, underscore, or hyphen.

/^[a-zA-Z0-9\_\-]{6,100}$/
^ asserts that we are at the beginning of the string
[a-zA-Z0-9_-] string can have any letter either uppercase , lowercase, numbers, underscores, or hyphens.
{6,100} matches a length of character having from 6 to 100
$ asserts that we are at the end of the string

Various RegEx explanation/testing tools.
1. Explain RegEx
2. RegEx101
3. Debuggex Demo
^[a-zA-Z0-9\_\-]{6,100}$

^ is an anchor. It asserts position at start of the string
[a-zA-Z0-9\_\-]{6,100} match a single character present in the list below
{6, 100}: Between 6 and 100 times, as many times as possible, giving back as needed
a-z a single character in the range between a and z (case sensitive)
A-Z a single character in the range between A and Z (case sensitive)
0-9 a single character in the range between 0 and 9
\_ matches the character _ literally
\- matches the character - literally
$ is an anchor. It asserts position at end of the string.
An alternative regex using flags would be:
/^[a-z\d\_\-]{6,100}$/i
Here \d matches digits (0-9), and flag i denotes case insensitivity.
This is what regular expressions do to perform matches, for starters:
(source: gyazo.com)