Base 26 convert

base26.js

'use strict';

const bigInt = require("big-integer");

function s26toi(s) {

    const base = 26;

    let ret = 0;
    let numl = String(s).length;
    let rev = 0;

    for (let i = numl - 1; i >= 0; i--) {
        let ton = bigInt(s.charAt(i).charCodeAt(0) - 97).multiply(bigInt(base).pow(rev));
        ret = bigInt(ret).add(ton);
        rev++;
    }

    return bigInt(ret);
}

function itos26(num) {

    const base = 26;

    let ret = "";
    let next = true;
    let i = 1;

    while (next) {

        let ton = parseInt(bigInt(num).mod(bigInt(base).pow(i)).divide(bigInt(base).pow(i-1)).toString());

        ret = `${b26(ton)}${ret}`;

        next = bigInt(num).mod(Math.pow(base, i)) != num;

        i++;
    }
    

    return ret;
}

function b26(num) {
    return String.fromCharCode(97 + num);
}

exports.s26toi = s26toi;
exports.itos26 = itos26;