Function to validate a CPF and CNPJ

isValidCNPJ.js

function isValidCNPJ(cnpj = '') {
    cnpj = `${cnpj}`.replace(/^\D+/gmi,  '')
 
    if (cnpj.length != 14 || new Set(cnpj).size === 1) return false
         
    size = cnpj.length - 2
    numbers = cnpj.substring(0, size)
    digits = cnpj.substring(size)
    soma = 0
    pos = size - 7
    for (i = size; i >= 1; i--) {
      soma += numbers.charAt(size - i) * pos--
      if (pos < 2)
            pos = 9
    }
    result = soma % 11 < 2 ? 0 : 11 - soma % 11

    if (result != digits.charAt(0)) return false
         
    size = size + 1
    numbers = cnpj.substring(0, size)
    soma = 0
    pos = size - 7
    for (i = size; i >= 1; i--) {
      soma += numbers.charAt(size - i) * pos--
      if (pos < 2)
            pos = 9
    }

    result = soma % 11 < 2 ? 0 : 11 - soma % 11
    if (result != digits.charAt(1)) return false
           
    return true
}

isValidCPF.js

function isValidCPF (cpf = '') {
    let sum = 0,
        remainder
        
    cpf = `${cpf}`.replace(/^\D+/gmi, '')

    if (cpf.length != 11 || new Set(cpf).size === 1) return false

    for (let i = 1; i <= 9; i++) sum = sum + parseInt(cpf.substring(i - 1, i)) * (11 - i)
    remainder = (sum * 10) % 11

    if (remainder == 10 || remainder == 11) remainder = 0
    if (remainder != parseInt(cpf.substring(9, 10))) return false

    sum = 0
    for (let i = 1; i <= 10; i++) sum = sum + parseInt(cpf.substring(i - 1, i)) * (12 - i)
    remainder = (sum * 10) % 11

    if (remainder == 10 || remainder == 11) remainder = 0
    if (remainder != parseInt(cpf.substring(10, 11))) return false

    return true
}