Código para comprobar un número de CUIT

checkCUIT.js

// https://es.wikipedia.org/wiki/Clave_%C3%9Anica_de_Identificaci%C3%B3n_Tributaria
// Expects the digits of the cuit except the last one (verifiying digit).
const getVerifiyingCUITDigit = (incompleteCUIT) => {
    const coefficients = [5, 4, 3, 2, 7, 6, 5, 4, 3, 2];

    if (incompleteCUIT.length !== coefficients.length) {
        return -1;
    }

    let totalSum = 0;

    for (let i = 0;
        i < coefficients.length;
        i += 1) {
        totalSum += parseInt(incompleteCUIT[i]) * coefficients[i];
    }

    const remainder = 11 - totalSum % 11;

    if (remainder === 11) {
        return 0;
    }

    if (remainder === 10) {
        return 1;
    }

    return remainder;
}

// Expects a CUIT with the format XX-XXXXXXXX-X
const isCUITValid = (cuit) => {
    if (!cuit) {
        return false;
    }

    const components = cuit.split("-");

    const types = ["20", "23", "24", "25", "26", "27", "30", "33", "34"];

    if (components.length != 3
        || !parseInt(components[0])
        || !parseInt(components[1])
        || !parseInt(components[2])
        || !types.includes(components[0])) {
        return false;
    }
    
    const expectedLastDigit = getVerifiyingCUITDigit(components[0] + components[1]);

    const lastDigit = parseInt(cuit[cuit.length - 1], 10);

    return expectedLastDigit === lastDigit;
}

module.exports = {
    isCUITValid, getVerifiyingCUITDigit
}