base62 encoding/decoding for integers in JavaScript

int62.js

(function() {
    // const
    var chars = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz',
        base = 62;

    window.int62 = function(int) {
        if (0 === int) {
            return '0';
        }

        var result = '', // let
            num = int,
            remainder;

        while (0 < num) {
            remainder = num % base;
            result = chars[remainder] + result;
            num = Math.floor(num / base);
        }

        return result;
    }

    window.unint62 = function(str) {
        var i, result = 0; // let

        for (i = 0; i < str.length; ++i) {
            result += chars.indexOf(str[str.length - 1 - i]) * Math.pow(base, i);
        }

        return result;
    }

})();

/*
// if you need BigInts, but this require ECMAScript 2020. Okay to use after 2025, should will be supported by ALL browsers.
function int62(int) { // aka base62_encode(integer)
    const chars = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';

    let result = '';
    let num = BigInt(int); // BigInt require ECMAScript 2020 (ES11)!

    if (num === 0n) {
        return chars[0];
    }

    while (num > 0n) {
        result = chars[num % 62n] + result;
        num = num / 62n;
    }

    return result;
}
*/