Instagram How to convert short code to media id two ways

ig_convert_shortcod_media_id.js

const bigint = require('big-integer')

const lower = 'abcdefghijklmnopqrstuvwxyz';
const upper = lower.toUpperCase();
const numbers = '0123456789'
const ig_alphabet = upper + lower + numbers + '-_'
const bigint_alphabet = numbers + lower

function toShortcode(longid) {
    const o = bigint(longid).toString(64)
    return o.replace(/<(\d+)>|(\w)/g, (m, m1, m2) => {
        return ig_alphabet.charAt((m1)
            ? parseInt(m1)
            : bigint_alphabet.indexOf(m2))
    });
}

function fromShortcode(shortcode) {
    const o = shortcode.replace(/\S/g, m => {
        const c = ig_alphabet.indexOf(m)
        const b = bigint_alphabet.charAt(c)
        return (b != "") ? b : `<${c}>`
    })
    return bigint(o, 64).toString(10)
}

console.log('2850692389359545326', toShortcode('2850692389359545326')); // s.b. 'ybyPRoQWzX'
console.log('CePsZ_fr2vu', fromShortcode('CePsZ_fr2vu')); // s.b. '908540701891980503'