JavaScript function that validates check digits for Brazilian CPF and CNPJ numbers

validateCnpjCpf.js

// Validates last two digits of a CPF or CNPJ
// Validation rules taken from http://ghiorzi.org/DVnew.htm
function validateCnpjCpf(value, type) {
    var cpf = (type === "cpf"),
        docLength = cpf ? 11 : 14,
        chkLast;

    if (value == null || value == "") {
        return true;
    }

    if (typeof value !== "string" || value.length > docLength) {
	    return false;
    }

    value = value.replace(/[^\d]+/g,'');
    while (value.length < docLength)
        value = "0" + value;

    chkLast = function(code) {
        var len = code.length - 1,
            sum = 0,
            mult = function(index) {
		return cpf ? 9 - (index % 10) : 9 - (index % 8);
	    };
            
        for (i = 0; i < len; i++) {
            sum += code.charAt(len - 1 - i) * mult(i);
        }

        var dv = sum % 11;
        dv = (dv == 10) ? 0 : dv;

        return dv == code.charAt(len);
    }

    return chkLast(value.slice(0,docLength-1)) && chkLast(value);    
}