TheAlgorithms/JavaScript · error · TypeError

argument is not a Number

Error message

argument is not a Number

What it means

Thrown by RGBToHex when any of r, g, or b is not of type 'number'. The guard checks all three with typeof; a single non-number argument (including NaN, which is technically typeof 'number' and will pass) triggers it. It is a TypeError.

Source

Thrown at Conversions/RGBToHex.js:3

function RGBToHex(r, g, b) {
  if (typeof r !== 'number' || typeof g !== 'number' || typeof b !== 'number') {
    throw new TypeError('argument is not a Number')
  }

  const toHex = (n) => (n || '0').toString(16).padStart(2, '0')

  return `#${toHex(r)}${toHex(g)}${toHex(b)}`
}

export { RGBToHex }

// > RGBToHex(255, 255, 255)
// '#ffffff'

// > RGBToHex(255, 99, 71)
// '#ff6347'

View on GitHub (pinned to 5c39e87a9a)

Solutions

1. Coerce channels with Number(...) or parseInt(..., 10) before calling.
2. Type-check all three in the caller: [r,g,b].every(v => typeof v === 'number' && !Number.isNaN(v)).
3. Keep a single source of truth for color values as numbers.

Example fix

// before
RGBToHex('255', 99, 71)
// after
RGBToHex(Number('255'), 99, 71)

if (![r, g, b].every((v) => typeof v === 'number' && !Number.isNaN(v))) {
  throw new TypeError('r, g, b must all be finite numbers')
}
RGBToHex(r, g, b)

const areRgbNumbers = (r, g, b) =>
  [r, g, b].every((v) => typeof v === 'number' && !Number.isNaN(v))

try {
  RGBToHex(r, g, b)
} catch (e) {
  if (e instanceof TypeError && /not a Number/.test(e.message)) {
    return RGBToHex(Number(r), Number(g), Number(b))
  }
  throw e
}

When it happens

Trigger: Calling RGBToHex('255', 0, 0) (r is a string), RGBToHex(null, 0, 0), or RGBToHex(undefined, 128, 128). Note NaN passes the guard because typeof NaN === 'number' — the function does not range-check.

Common situations: Reading color channels from a form/JSON where they arrive as strings; passing a value that was never initialized (undefined); mixing a defaulted optional channel.

Related errors

• Only string arguments are allowed
• Argument is not a string type
• Argument is not a string.
• Input is not a valid RGB color.
• hue should be between 0 and 360

AI-assisted analysis of TheAlgorithms/JavaScript@5c39e87a9a (2026-08-13). Data as JSON: /api/errors/5fb85814e1ec59bc. Report an issue: GitHub.