JavaScript regex - Validate Credit Card in JS

Last Updated : 19 Nov, 2024

To validate a credit card number in JavaScript we will use regular expression combined with Luhn's algorithm. Appling Luhn's algorithm to perform a checksum validation for added security

Luhn algorithm:

  • It first sanitizes the input by removing any non-digit characters (e.g., spaces).
  • It then processes the digits from the end, doubling every second digit, and subtracting 9 if the doubled value is greater than 9.
  • The sum of all digits is calculated, and if the sum is divisible by 10, the card is valid.
JavaScript 
function validCard(n) {
    // Remove all non-num characters (e.g., spaces or hyphens)
    const s = n.replace(/[^0-9]/g, '');

    // Check if the input length is valid (most cards have between 13 and 19 nums)
    if (s.length < 13 || s.length > 19) {
        return false;
    }

    let sum = 0;
    let sd = false;

    // Loop through the card number nums, starting from the last num
    for (let i = s.length - 1; i >= 0; i--) {
        let num = parseInt(s[i], 10);

        if (sd) {
            num *= 2;
            if (num > 9) {
                num -= 9; // If the result is a two-num number, subtract 9
            }
        }

        sum += num;
        sd = !sd; // Toggle the doubling
    }

    // If the total sum is divisible by 10, it's a valid card number
    return sum % 10 === 0;
}

const n = '4539 1488 0343 6467'; // Example Visa number
if (validCard(n)) {
    console.log('Valid credit card number.');
} else {
    console.log('Invalid credit card number.');
}

Output
Valid credit card number.

Luhn algorithm validates only the format. But How to check on the card was from which company.

Determining the Credit Card Issuer

JavaScript 
function getIssuer(num) {
    // Remove all non-digit characters (e.g., spaces or hyphens)
    const s = num.replace(/[^0-9]/g, '');

    // Check the length of the card number
    if (s.length < 13 || s.length > 19) {
        return 'Invalid card length';
    }

    // Determine the card issuer
    if (/^4/.test(s)) {
        return 'Visa';
    } else if (/^5[1-5]/.test(s)) {
        return 'MasterCard';
    } else if (/^3[47]/.test(s)) {
        return 'American Express';
    } else if (/^6(?:011|5)/.test(s)) {
        return 'Discover';
    } else if (/^3(?:0[0-5]|[68])/.test(s)) {
        return 'Diners Club';
    } else if (/^35/.test(s)) {
        return 'JCB';
    } else {
        return 'Unknown issuer';
    }
}

const num = '4111 1111 1111 1111';
console.log(`The card issuer is: ${getIssuer(num)}`);

Output
The card issuer is: Visa

Explanation credit card issuer:

  • Visa cards start with the digit 4.
  • Master Card cards typically start with numbers ranging from 51 to 55.
  • American Express (Amex) cards start with 34 or 37.
  • Discover cards may start with 6011 or have other prefixes starting with 65.
  • Diners Club cards can start with specific ranges such as 300-305, 36, or 38.
  • JCB cards often start with 35.
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