HexToBinary.js

const binLookup = (key) => ({
 0: '0000',
 1: '0001',
 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