TheAlgorithms/JavaScript · error · Error

Invalid hex string.

Error message

Invalid hex string.

What it means

Thrown by hexToInt (used by hexToDecimal) when hexNum does not match /^[0-9A-F]+$/, i.e. it must be non-empty and contain ONLY uppercase A-F and digits. This is stricter than HexToBinary: lowercase hex, a '0x' prefix, empty string, or any non-hex char all fail. Plain Error (content validation, not type).

Source

Thrown at Conversions/HexToDecimal.js:3

function hexToInt(hexNum) {
  if (!/^[0-9A-F]+$/.test(hexNum)) {
    throw new Error('Invalid hex string.')
  }
  const numArr = hexNum.split('') // converts number to array
  return numArr.map((item, index) => {
    switch (item) {
      case 'A':
        return 10
      case 'B':
        return 11
      case 'C':
        return 12
      case 'D':
        return 13
      case 'E':
        return 14
      case 'F':
        return 15
      default:
        return parseInt(item)

View on GitHub (pinned to 5c39e87a9a)

Solutions

1. Uppercase and strip prefixes: const clean = hex.toUpperCase().replace(/^0x/, '').
2. Validate with /^[0-9A-F]+$/ before calling.
3. Handle empty input upstream instead of forwarding '' to the converter.

Example fix

// before
hexToDecimal('ff')
// after
hexToDecimal('ff'.toUpperCase())

const clean = String(hexNum).replace(/^0x/i, '').toUpperCase()
if (!/^[0-9A-F]+$/.test(clean)) {
  throw new Error('Invalid hex string')
}
return hexToDecimal(clean)

const isValidUpperHex = (s) =>
  typeof s === 'string' && /^[0-9A-F]+$/.test(s)

try {
  hexToDecimal(hexNum)
} catch (e) {
  if (/Invalid hex string/.test(e.message)) {
    return hexToDecimal(String(hexNum).replace(/^0x/i, '').toUpperCase())
  }
  throw e
}

When it happens

Trigger: Calling hexToDecimal('ff') (lowercase rejected), hexToDecimal('0xFF') (prefix + lowercase), hexToDecimal('') (empty fails the + quantifier), or hexToDecimal('GG').

Common situations: Lowercase hex from CSS colors (#ffffff) or JSON; values prefixed with '0x' from language literals; empty string from a missing field; lowercase output of another function fed in here.

Related errors

• Argument is not a valid HEX code!
• Duplicate characters in character set are not allowed
• Not a valid character: ${digit}
• Argument is not a string type
• Invalid units

AI-assisted analysis of TheAlgorithms/JavaScript@5c39e87a9a (2026-08-13). Data as JSON: /api/errors/f0d24b6da012b429. Report an issue: GitHub.