Convert from Instagram Shortcode to Id and Back using big-integer

InstagramIdConvert.js

var bigint = require( 'big-integer' )

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

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

toShortcode(  '908540701891980503' ) // s.b. 'ybyPRoQWzX'
fromShortcode( 'ybyPRoQWzX' ) // s.b. '908540701891980503'

and obviously shortcode generated from this is wrong. Tried to find solution for that whole day, but it seems that Instagram API is just unusable crap, no wonder so many brutal Instagram scrapers arrived at npm within last two years :(

Hey @jamzy118 did you find a solution to your problem ?
I have the exact same.

I post a media through the Graph API and it answers me an ID, but the shortcode generated from this ID is wrong.
Received ID : 17889455560051444
Incorrect shortcode from this ID : _dxrQnDeT
Correct shortcode : CSZUyULIgWQ
ID from this shortcode : 2637230475367810448

Same problem as pierrocknroll ^

Same here. Spent 2 days trying to fix this basic conversion which FB could do it for us. It makes total sense.