TheAlgorithms/JavaScript · error · Error

${creditCardString} is an invalid credit card number because

Error message

${creditCardString} is an invalid credit card number because of its length.

What it means

Thrown by validateCreditCard() after the type and NaN checks pass, when the string's length is not between 13 and 16 inclusive. This is a generic Error (not TypeError) because the value is well-formed data that fails a business rule. Most card networks issue numbers in this length range.

Source

Thrown at String/ValidateCreditCard.js:47

  })

  return validationSum % 10 === 0
}

const validateCreditCard = (creditCardString) => {
  const validStartSubString = ['4', '5', '6', '37', '34', '35'] // Valid credit card numbers start with these numbers

  if (typeof creditCardString !== 'string') {
    throw new TypeError('The given value is not a string')
  }

  const errorMessage = `${creditCardString} is an invalid credit card number because `
  if (isNaN(creditCardString)) {
    throw new TypeError(errorMessage + 'it has nonnumerical characters.')
  }
  const creditCardStringLength = creditCardString.length
  if (!(creditCardStringLength >= 13 && creditCardStringLength <= 16)) {
    throw new Error(errorMessage + 'of its length.')
  }
  if (
    !validStartSubString.some((subString) =>
      creditCardString.startsWith(subString)
    )
  ) {
    throw new Error(errorMessage + 'of its first two digits.')
  }
  if (!luhnValidation(creditCardString)) {
    throw new Error(errorMessage + 'it fails the Luhn check.')
  }

  return true
}

export { validateCreditCard }

View on GitHub (pinned to 5c39e87a9a)

Solutions

  1. Confirm the expected length range (13–16 digits) for the card network you target.
  2. Re-check that your sanitizer removed only separators, not digits: raw.replace(/[\s-]/g, '') (not /\D/g if you have legitimate concerns — though digits are what you want).
  3. Show a length hint to the user in the form ('Card number must be 13–16 digits').
  4. Log the sanitized length during debugging to see what reached the validator.

Example fix

// before
validateCreditCard(raw) // length mismatch after a buggy sanitizer

// after
const digits = raw.replace(/[\s-]/g, '')
if (digits.length >= 13 && digits.length <= 16) {
  validateCreditCard(digits)
} else {
  // surface a user-facing length error
}
Defensive patterns

Strategy: validation

Validate before calling

function validateCardLength(v) {
  const digits = String(v).replace(/\D/g, '')
  if (digits.length < 13 || digits.length > 16) {
    throw new Error('card number must be 13-16 digits')
  }
  return validateCreditCard(digits)
}

Type guard

const hasCardLength = (s) => typeof s === 'string' && s.length >= 13 && s.length <= 16

Try / catch

try { validateCreditCard(card) } catch (e) { if (/of its length/.test(e.message)) { /* prompt user to re-enter */ } else throw e }

Prevention

When it happens

Trigger: Calling validateCreditCard('4532015112830') (12 digits, too short), validateCreditCard('4532015112830366789') (19 digits, too long), validateCreditCard('4') (1 digit), or any digit-only string whose length falls outside [13,16]. A stripped input that lost digits during sanitization commonly lands here.

Common situations: User mistyped or dropped digits; aggressive sanitizer stripped legitimate digits (e.g. removed 0s); a non-card number (e.g. CVV, ZIP) accidentally routed into validation; concatenating card fields incorrectly.

Related errors

AI-assisted analysis of TheAlgorithms/JavaScript@5c39e87a9a (2026-08-13). Data as JSON: /api/errors/a8efe42babf5ecbc. Report an issue: GitHub.