TheAlgorithms/JavaScript · error · Error

Argument is not a valid HEX code!

Error message

Argument is not a valid HEX code!

What it means

Thrown by hexToBinary when hexString contains any character that is not a hex digit. The regex /[^\da-f]/gi allows only 0-9 and a-f/A-F; anything else (spaces, 0x prefix, 'g'-'z', punctuation) triggers it. Note this is a plain Error, not a TypeError, because the type is correct but the content is invalid.

Source

Thrown at Conversions/HexToBinary.js:27

    6: '0110',
    7: '0111',
    8: '1000',
    9: '1001',
    a: '1010',
    b: '1011',
    c: '1100',
    d: '1101',
    e: '1110',
    f: '1111'
  })[key.toLowerCase()] // select the binary number by valid hex key with the help javascript object

const hexToBinary = (hexString) => {
  if (typeof hexString !== 'string') {
    throw new TypeError('Argument is not a string type')
  }

  if (/[^\da-f]/gi.test(hexString)) {
    throw new Error('Argument is not a valid HEX code!')
  }
  /*
    Function for converting Hex to Binary

    1. We convert every hexadecimal bit to 4 binary bits
    2. Conversion goes by searching in the lookup table
  */

  return hexString.replace(/[0-9a-f]/gi, (lexeme) => binLookup(lexeme))
}

export default hexToBinary

View on GitHub (pinned to 5c39e87a9a)

Solutions

1. Strip prefixes/separators first: hexString.replace(/^0x/i, '').replace(/[^0-9a-f]/gi, '').
2. Trim whitespace and newlines before calling.
3. Validate with /^[0-9a-f]+$/i.test(input) and reject early with a clearer message.

Example fix

// before
hexToBinary('0xFF')
// after
hexToBinary('0xFF'.replace(/^0x/i, ''))

const clean = String(hexString).replace(/^0x/i, '').replace(/[^0-9a-f]/gi, '')
if (!clean) throw new Error('No valid hex digits')
return hexToBinary(clean)

const isValidHex = (s) => typeof s === 'string' && /^[0-9a-f]+$/i.test(s)

try {
  hexToBinary(hexString)
} catch (e) {
  if (/not a valid HEX code/.test(e.message)) {
    return hexToBinary(hexString.replace(/^0x/i, '').trim())
  }
  throw e
}

When it happens

Trigger: Calling hexToBinary('0xFF') (the 'x' is invalid), hexToBinary('ff ff') (space), hexToBinary('gg'), or hexToBinary('#ffffff') (the '#' fails). Even a trailing newline will trip it.

Common situations: Input carries a '0x' prefix from a formatter; pasted values include spaces or a leading '#'; CRLF newlines from a file line; mixed notation like 'hFF'.

Related errors

• Invalid hex string.
• 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/e79595e918cdf402. Report an issue: GitHub.