TheAlgorithms/JavaScript · error · TypeError

Argument is not a string type

Error message

Argument is not a string type

What it means

Thrown by hexToBinary when hexString is not of type 'string'. This is the first guard in the function and runs before the hex-validity regex. It is a TypeError (not a plain Error) because the contract is about the argument type, not its content.

Source

Thrown at Conversions/HexToBinary.js:23

    2: '0010',
    3: '0011',
    4: '0100',
    5: '0101',
    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. Coerce to string with String(...) only if the value is genuinely hex text, e.g. String(hexValue).
2. If you have a Buffer/Uint8Array, convert with buf.toString('hex') first.
3. Add a typeof hexString === 'string' guard in the caller and surface a clearer error.

Example fix

// before
hexToBinary(someBuffer)
// after
hexToBinary(someBuffer.toString('hex'))

if (typeof hexString !== 'string') {
  throw new TypeError('hexString must be a string')
}
hexToBinary(hexString)

const isString = (x) => typeof x === 'string'

try {
  hexToBinary(hexString)
} catch (e) {
  if (e instanceof TypeError && /not a string type/.test(e.message)) {
    return hexToBinary(String(hexString))
  }
  throw e
}

When it happens

Trigger: Calling hexToBinary(255), hexToBinary(null), hexToBinary(['a','b']), or hexToBinary(Buffer.from('ab','hex')) — none of these are strings.

Common situations: Passing a Node.js Buffer or Uint8Array thinking it is a string; feeding a parsed JSON number; forgetting to coerce a DOM input value; defaulting the argument to undefined.

Related errors

• Only string arguments are allowed
• Argument is not a string.
• argument is not a Number
• Argument str should be String
• Argument should be string

AI-assisted analysis of TheAlgorithms/JavaScript@5c39e87a9a (2026-08-13). Data as JSON: /api/errors/63b66b150b37165c. Report an issue: GitHub.