ic-validator/lib/index.js

Simple Typescript/Javascript validator for Czech business identification number (IČ)

export default function isValid(ic) {
    if (!ic) {
        return false;
    }
    if (typeof ic === "number") {
        ic = ic.toString();
    }
    // Prepend zeros for older format of identification number, which has fewer digits
    if (ic.length < 8) {
        ic = ic.padStart(8, "0");
    }
    if (ic.length !== 8) {
        return false;
    }
    // Get all digits which are used to calculate checksum digit (omit last digit)
    const digits = [...ic].slice(0, 7);
    // Calculate weighted sum
    const sum = digits.reduce((acc, val, i) => acc + Number(val) * (8 - i), 0);
    if (Number.isNaN(sum)) {
        throw Error(`IČ with value ${ic}, couldn't be parsed during validation`);
    }
    // Calculate checksum and check if is equal to passed IC
    return ((11 - (sum % 11)) % 10).toString() === ic.charAt(7);
}