Digito verificador em PHP e Javascript

mod11.js

/**
 * Calculates the Modulo 11 for generating the verification digit of bank slips and bank accounts.
 * 
 * @author Pablo Costa <pablo@users.sourceforge.net>
 * @link www.febraban.org.br
 * 
 * @param {string} num Numeric string for which the verification digit is to be calculated.
 * @param {number} [base=9] Maximum value of multiplication.
 * @param {number} [r=0] Specifies the return type. If 0, returns the verification digit, if 1 returns the remainder.
 * 
 * @returns {number} Returns the verification digit or remainder based on the r parameter.
 * 
 * @note Script developed without any reuse of pre-existing code.
 * @note It's assumed that the verification of the format of the input variables is done before executing this script.
 */
function modulo11(num, base = 9, r = 0) {
    let sum = 0;
    let factor = 2;

    // Separation of numbers
    for (let i = num.length; i > 0; i--) {
        // Get each number individually
        let currentNum = parseInt(num.charAt(i - 1));
        
        // Multiply the number by the factor
        let partial = currentNum * factor;

        // Sum of the digits
        sum += partial;

        if (factor === base) {
            // Reset multiplication factor to 2
            factor = 1;
        }

        factor++;
    }

    // Calculation of modulo 11
    if (r === 0) {
        sum *= 10;
        let digit = sum % 11;

        if (digit === 10) {
            digit = 0;
        }

        return digit;
    } else if (r === 1) {
        let remainder = sum % 11;
        return remainder;
    }
}

mod11.php

<?php
/**
 * Calculates the Modulo 11 for generating the verification digit of bank slips and bank accounts.
 * 
 * @author Pablo Costa <pablo@users.sourceforge.net>
 * @link www.febraban.org.br
 * 
 * @param string $num Numeric string for which the verification digit is to be calculated.
 * @param int $base Maximum value of multiplication. Defaults to 9.
 * @param int $r Specifies the return type. If 0, returns the verification digit, if 1 returns the remainder. Defaults to 0.
 * 
 * @return int Returns the verification digit or remainder based on the $r parameter.
 * 
 * @note Script developed without any reuse of pre-existing code.
 * @note It's assumed that the verification of the format of the input variables is done before executing this script.
 */
function modulo_11($num, $base = 9, $r = 0) {
    $sum = 0;
    $factor = 2;

    // Separation of numbers
    for ($i = strlen($num); $i > 0; $i--) {
        // Get each number individually
        $numbers[$i] = substr($num, $i - 1, 1);
        // Multiply the number by the factor
        $partial[$i] = $numbers[$i] * $factor;
        // Sum of the digits
        $sum += $partial[$i];

        if ($factor == $base) {
            // Reset multiplication factor to 2
            $factor = 1;
        }

        $factor++;
    }

    // Calculation of modulo 11
    if ($r == 0) {
        $sum *= 10;
        $digit = $sum % 11;

        if ($digit == 10) {
            $digit = 0;
        }

        return $digit;
    } elseif ($r == 1) {
        $remainder = $sum % 11;
        return $remainder;
    }
}