RGBToHex.js

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'