TheAlgorithms/JavaScript · error · TypeError

${creditCardString} is an invalid credit card number because

Error message

${creditCardString} is an invalid credit card number because it has nonnumerical characters.

What it means

Thrown by validateCreditCard() when the string passes the type check but isNaN(creditCardString) is true — i.e. the string contains characters that are not parseable as a number (spaces, dashes, letters). A TypeError, because the function expects a pure-digit string. The interpolated value is echoed into the message.

Source

Thrown at String/ValidateCreditCard.js:43

        currentDigit += 1
      }
    }
    validationSum += currentDigit
  })

  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
}

View on GitHub (pinned to 5c39e87a9a)

Solutions

1. Strip non-digit characters before validating: validateCreditCard(raw.replace(/\D/g, '')).
2. Normalize input: remove spaces and dashes, e.g. raw.replace(/[\s-]/g, '').
3. Validate digit-only upstream with /^\d+$/.test(normalized) before calling.
4. Reject obviously malformed input at the form layer with an inputmode='numeric' field.

Example fix

// before
validateCreditCard(cardField.value) // '4532-0151-1283-0366'

// after
const digits = cardField.value.replace(/\D/g, '')
validateCreditCard(digits)

function validateCardNormalized(v) {
  if (typeof v !== 'string') throw new TypeError('not a string')
  const digits = v.replace(/\D/g, '')
  if (!/^\d+$/.test(digits)) throw new TypeError('nonnumerical characters')
  return validateCreditCard(digits)
}

const isAllDigits = (s) => typeof s === 'string' && /^\d+$/.test(s)

try { validateCreditCard(card) } catch (e) { if (/nonnumerical/.test(e.message)) { card = card.replace(/\D/g, ''); /* retry */ } else throw e }

When it happens

Trigger: Calling validateCreditCard('4532-0151-1283-0366') (dashes), validateCreditCard('4532 0151 1283 0366') (spaces), validateCreditCard('4532abcd12830366'), validateCreditCard(''), validateCreditCard('not-a-card'). An empty string isNaN('') === false, so '' will NOT throw here — but a whitespace-only or alphabetic string will.

Common situations: Users typing card numbers with spaces/dashes; formatters that group digits with separators; copy-paste from a formatted source; forgetting to strip whitespace from raw input before validation.

Related errors

• The given value is not a string
• The arg must be a valid, non empty string
• The given value is not a string
• The given value is not a string
• ${creditCardString} is an invalid credit card number because

AI-assisted analysis of TheAlgorithms/JavaScript@5c39e87a9a (2026-08-13). Data as JSON: /api/errors/a696e545e6593e7f. Report an issue: GitHub.