What is an example of a matching and non-matching string?

A valid matching string is "4111111111111111". A non-matching string is "5111111111111111".

Is this regex safe from ReDoS (Catastrophic Backtracking)?

Yes, this pattern is optimized for linear execution time and safe for browser-side validation without locking up the UI thread.

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Visa Credit Card Number Regex

Q: How do I test this regex in JavaScript and TypeScript?

Use regex.test(): const regex = /^4[0-9]{12}(?:[0-9]{3})?$/; const isValid = regex.test(inputString);

Matches 13-digit and standard 16-digit Visa debit and credit card numbers starting with 4.

Regular Expression Pattern:

/^4[0-9]{12}(?:[0-9]{3})?$/

Valid Match Example:

4111111111111111

Invalid / Non-Match Example:

5111111111111111

Regex Syntax Breakdown & Explanation

•^4 : Visa Issuer Identification Number (IIN) always begins with digit 4
•[0-9]{12} : Base 12 digits
•(?:[0-9]{3})?$ : Optional 3 additional digits for standard 16-digit cards

Implementation in Popular Languages

JavaScript / TypeScript

const regex = /^4[0-9]{12}(?:[0-9]{3})?$/;
const isValid = regex.test("4111111111111111");
console.log(isValid); // true

Python (re)

import re

pattern = r"^4[0-9]{12}(?:[0-9]{3})?$"
match = re.match(pattern, "4111111111111111")
print(bool(match)) # True

Go (regexp)

package main
import (
  "fmt"
  "regexp"
)

func main() {
  re := regexp.MustCompile(`^4[0-9]{12}(?:[0-9]{3})?$`)
  fmt.Println(re.MatchString("4111111111111111"))
}

Frequently Asked Questions

Everything you need to know regarding specifications, syntax, and security best practices.

The regular expression pattern is /^4[0-9]{12}(?:[0-9]{3})?$/. Matches 13-digit and standard 16-digit Visa debit and credit card numbers starting with 4.