isValidServiceId.js

const isValidServiceId = (serviceId) => {

    serviceId = `${serviceId}`;
    while (serviceId.length < 10) {
        serviceId = `0${serviceId}`;
    }

    const rootId = serviceId.slice(0, -1);

    let sum = 0;
    for (let i = 0, index = rootId.length + 1; i < rootId.length; i++, index--) {

        sum += parseInt(rootId[i]) * index;
    }

    const value = (11 - sum % 11) % 11;

    return serviceId[9] === (value === 10 ? 'X' : value);
};