Função JavaScript para validar CNPJ

validaCNPJ.js

function validaCNPJ (cnpj) {
    var b = [ 6, 5, 4, 3, 2, 9, 8, 7, 6, 5, 4, 3, 2 ]
    var c = String(cnpj).replace(/[^\d]/g, '')
    
    if(c.length !== 14)
        return false

    if(/0{14}/.test(c))
        return false

    for (var i = 0, n = 0; i < 12; n += c[i] * b[++i]);
    if(c[12] != (((n %= 11) < 2) ? 0 : 11 - n))
        return false

    for (var i = 0, n = 0; i <= 12; n += c[i] * b[i++]);
    if(c[13] != (((n %= 11) < 2) ? 0 : 11 - n))
        return false

    return true
}