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Regex for String in React

How shall we write a regular expression to validate a string that should have a length of a minimum of 1 character and a maximum of 50 characters, have both upper case and lower case, alphanumeric, include space, and have mostly used special characters like #,._-&$#? The first character should be either alphabet or number then the rest can be as mentioned above.
*If it is only one character then it should be an alphanumeric one
I have tried a regex with my limited knowledge which looks like
^[a-zA-z]*[a-zA-Z\d\-_#&$%#\s]{1,50}$
But I am not able to match the string if there is only one character given, can anyone guide me to fix this

You can use
/^(?=[\p{L}0-9])[\p{L}\p{N}_#,.&$%#\s-]{1,50}$/u
See the regex demo
Details
^ - start of string
(?=[\p{L}0-9]) - the first char must be a Unicode letter (\p{L}) or an ASCII digit
[\p{L}\p{N}_#,.&$%#\s-]{1,50} - one to fifty
\p{L} - any Unicode letter
\p{N} - any Unicode digit
_#,.&$%#- - any of these chars
\s - any whitespace
$ - end of string.

Issues in password regular expression

Hi all I am making a password regular expression in javascript test() method, It will take the following inputs
solution
/^(?=.*\d)^(?=.*[!#$%'*+\-/=?^_{}|~])(?=.*[A-Z])(?=.*[a-z])\S{8,15}$/gm
May contains any letter except space
At least 8 characters long but not more the 15 character
Take at least one uppercase and one lowercase letter
Take at least one numeric and one special character
But I am not able to perform below task with (period, dot, fullStop)
(dot, period, full stop) provided that it is not the first or last character, and provided also that it does not appear two or more times consecutively.
Can anyone one help me to sort out this problem, Thanks in advance

You may move the \S{8,15} part with the $ anchor to the positive lookahead and place it as the first condition (to fail the whole string if it has spaces, or the length is less than 8 or more than 15) and replace that pattern with [^.]+(?:\.[^.]+)* consuming subpattern.
/^(?=\S{8,15}$)(?=.*\d)(?=.*[!#$%'*+\/=?^_{}|~-])(?=.*[A-Z])(?=.*[a-z])[^.]+(?:\.[^.]+)*$/
See the regex demo
Details:
^ - start of string
(?=\S{8,15}$) - the first condition that requires the string to have no whitespaces and be of 8 to 15 chars in length
(?=.*\d) - there must be a digit after any 0+ chars
(?=.*[!#$%'*+\/=?^_{}|~-]) - there must be one symbol from the defined set after any 0+ chars
(?=.*[A-Z]) - an uppercase ASCII letter is required
(?=.*[a-z]) - a lowercase ASCII letter is required
[^.]+(?:\.[^.]+)* - 1+ chars other than ., followed with 0 or more sequences of a . followed with 1 or more chars other than a dot (note that we do not have to add \s into these 2 negated character classes as the first lookahead already prevalidated the whole string, together with its length)
$ - end of string.

Regex which accepts alphanumerics only, except for one hyphen in the middle

I am trying to construct a regular expression which accepts alphanumerics only ([a-zA-Z0-9]), except for a single hyphen (-) in the middle of the string, with a minimum of 9 characters and a maximum of 20 characters.
I have verified the following expression, which accepts a hyphen in the middle.
/^[a-zA-Z0-9]+\-?[a-zA-Z0-9]+$/
How can I set the minimum 9 and maximum 20 characters for the above regex? I have already used quantifiers + and ? in the above expression.
How would I apply {9,20} to the above expression? Are there any other suggestions for the expression?

/^[a-zA-Z0-9]+\-?[a-zA-Z0-9]+$/
can be simplified to
/^[a-z0-9]+(?:-[a-z0-9]+)?$/i
since if there is no dash then you don't need to look for more letters after it, and you can use the i flag to match case-insensitively and avoid having to reiterate both lower-case and upper-case letters.
Then split your problem into two cases:
9-20 alpha numerics
10-21 characters, all of which are alpha numerics except one dash
You can check the second using a positive lookahead like
/^(?=.{10,21}$)/i
to check the number of characters without consuming them.
Combining these together gives you
/^(?:[a-z0-9]{9,20}|(?=.{10,21}$)[a-z0-9]+-[a-z0-9]+)$/i

You can do this provided you don't want - to be present exactly in middle
/^(?=[^-]+-?[^-]+$)[a-zA-Z\d-]{9,20}$/
[^-] matches any character that is not -

Validating phone number using regex with support for multuple numbers

I am not very experienced with regex and I need to validate phone numbers using javascript.
I have a textbox which need to be allowed to accept multiple phone numbers with a delimiter of ';' and the characters that can be allowed for the phone numbers are
Numbers
'+'
'-'
Could someone help me on how I can acheive this using javascript and regex/ regular expressions?
Example:
+91-9743574891;+1-570-456-2233;+66-12324576
I tried the following:
^[0-9-+;]+$
Am not sure if this is correct.

You have placed - in wrong place so, your regex is not working.
Try this(your RegEx, but slightly modified):
^[0-9+;-]+$
or
^[-0-9+;]+$
To include a hyphen within a character class then you must do one of the following:
escape the hyphen and use \-,
place hyphen either at the beginning or at the end of the character class.
As the hyphen is used for specifying a range of characters. So, regex engine understands [0-9-+;]+ match any of the characters between 0 to 9, 9 to +(all characters having decimal code-point 57[char 9] to 43[char +] and it fails) and ;.

To be a bit more restrictive, you could use the following regexp:
/^\+[0-9]+(-[0-9]+)+(;\+[0-9]+(-[0-9]+)+)*$/
What it will match:
+91-9743574891
+1-570-456-2233;+66-12324576
What it won't match:
91-9743574891
+15704562233
6612324576

How about this ^([0-9\-\+]{5,15};?)+$
Explanation:
^ #Match the start of the line
[0-9\-\+] #Allow any digit or a +/- (escaped)
{5,15} #Length restriction of between 5 and 15 (change as needed)
;? #An optional semicolon
+ #Pattern can be repeat once or more
$ #Until the end of the line
Only as restrictive as specified could be tighter, See it working here.

Your regex will match what you allow, but I would be a bit more restrictive:
^\+?[0-9-]+(?:;\+?[0-9-]+)*$
See it here on Regexr
That means match an optional "+" followed by a series of digits and dashes. Then there can be any amount of additional numbers starting with a semicolon, then the same pattern than for the first number.

Regex to match card code input

How can I write a regex to match strings following these rules?
1 letter followed by 4 letters or numbers, then
5 letters or numbers, then
3 letters or numbers followed by a number and one of the following signs: ! & # ?
I need to allow input as a 15-character string or as 3 groups of 5 chars separated by one space.
I'm implementing this in JavaScript.

I'm not going to write out the whole regex for you since this is homework, but here are some hints which should help you out:
Use character classes. [A-Z] matches all uppercase. [a-z] matches all lowercase. [0-9] matches numbers. You can combine them like so [A-Za-z0-9].
Use quantifiers like {n} so [A-Z]{3} gives you 3 uppercase letters.
You can put other characters in character classes. Let's say you wanted to match % or # or #, you could do [%##] which would match any of those characters.
Some meta-characters (characters which have special meaning in the context of regular expressions) will need to be escaped like so: \$ (since $ matches the end of a line)
^ and $ match the beginning and end of the line respectively.
\s matches white-space, but if you sanitize your input, you shouldn't need to use this.
Flags after the regex do special things. For example in /[a-z]/i, the i ignores case.

This should be it:
/^[a-z][a-z0-9]{4} ?[a-z0-9]{5} ?[a-z0-9]{3}[0-9][!&#?]$/i
Feel free to change 0-9 and [0-9] with \d if you see fit.
The regex is simple and readable enough. ^ and $ make sure this is a whole match, so there aren't extra characters before or after the code, and the /i flag allows upper or lower case letters.

I would start with a tutorial.
Pay attention to the quantifiers (like {N}) and character classes (like [a-zA-Z])

^[a-zA-Z][a-zA-Z0-9]{4} ?[a-zA-Z0-9]{5} ?[a-zA-Z0-9]{3}[\!\&\#\?]$