CPF Refatorado

cpfRefatorado.js

const getDigit = ( cpf ) => cpf.slice( 9 )
const mod11 = ( num ) => num % 11
const generateArrayOfLength = ( length ) => Array.from( { length }, ( v, k ) => k )
const invalidCpfs = generateArrayOfLength( 10 ).map( val => `${ val }`.repeat( 11 ) )
const isEqual = ( val1 ) => ( val2 ) => val1 === val2
const isIn = ( list ) => ( num ) => list.findIndex( isEqual( num ) ) >= 0
const isInInvalidCpf = isIn( invalidCpfs )
const NOT = ( val ) => !val
const getCpfAsArrayWithoutDigit = ( cpf ) => cpf.split( '' ).slice( 0, 9 )
const calcSumDigit = ( multiplier, digit, sum ) => sum + ( digit * multiplier )

const calculateSums = ( multiplier ) => ( [ sum2, sum1 ] , currentNum ) =>
  [ calcSumDigit( multiplier--, currentNum, sum2 ), calcSumDigit( multiplier, currentNum, sum1 ) ]

/*
O calculo de calculateDigit foi alterado, baseando-se no item 4:
4) Caso o valor do resto da divisão seja menor que 2,
 esse valor passa automaticamente a ser zero, 
 caso contrário é necessário subtrair o valor obtido
 de 11 para se obter o dígito verificador.
Fonte: http://www.geradorcpf.com/algoritmo_do_cpf.htm
*/
const calculateDigit = ( num ) => ( mod11( num ) < 2 ? 0 : 11 - mod11( num ) )
const concatDigits = ( firstDigit, secondDigit ) => 
  (firstDigit !== 0)
  ? ( firstDigit * 10 ) + secondDigit + ''
  : '0' + secondDigit

const generateDigit = ( previousNum, currentNum ) => 
  ( previousNum === null )
  ? calculateDigit( currentNum ) 
  : concatDigits( previousNum, calculateDigit( ( previousNum * 2) + currentNum ) )

const isCpfRight = ( cpf ) =>
    getCpfAsArrayWithoutDigit( cpf )
      .reduce( calculateSums( 11 ), [ 0, 0 ] )
      .reverse().reduce( generateDigit, null ) === getDigit( cpf )

const validate = ( cpf ) => ( NOT( isInInvalidCpf( cpf ) ) && isCpfRight( cpf ) )

const CPFS = [
  '04998264931', '03506838326',
  '03506838321', '22222222222', 
  '00000000000', '04864713901'
]

CPFS.forEach( ( cpf ) => console.log( `${ cpf }: ${ validate( cpf ) }` ) )