@edyspider/validate-niss/src/index.js

A NPM package to validate Portuguese social security identification number (NISS).

function validateNISS(value) {
    // Check if it is null
    if (value === null) {
        return false;
    }

    // Check if the input is exactly 11 characters long and contains only digits
    if (!/^\d{11}$/.test(value)) {
        return false;
    }

    // Check first digit
    if (value[0] === '0') {
        return false;
    }

    // Ensure the input is a string
    if (typeof value !== 'string') {
        return false;
    }

    // Set calculation variables
    factor = ['29', '23', '19', '17', '13', '11', '7', '5', '3', '2'];

    // Factor calculation
    calc = 0;
    for (i = 0; i < 10; i++) {
        calc += value[i] * factor[i];
    }

    // Calculate MOD 10
    const mod10 = calc % 10;
    
    //Calculate check digit
    const checkSum = 9 - mod10;

    // Compare calculated check digit with the provided one
    const checkDigit = (value % 10);
    return (checkSum === checkDigit);
}

module.exports = validateNISS;