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JavaScript regex - Validate Credit Card in JS

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.

JavaScript regex - Validate Credit Card in JS

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