Issue when importing typescript src

[yelhouti]

I would like to use this lib on my typescript project. Sadly, types are not exported.
And when i try to import from:

import ThermalPrinter, { PrinterTypes } from 'browser-thermal-printer/src/core';

My typescript fails because my project has stricter rules.

Error: node_modules/browser-thermal-printer/src/interfaces/epson/epson.ts:251:30 - error TS2769: No overload matches this call.
The last overload gave the following error.
Type 'string | undefined' is not assignable to type 'string'.
Type 'undefined' is not assignable to type 'string'.
Type 'number' is not assignable to type 'string'.
251 this.append(Buffer.from([type, data.length]));

Is there away to export the.d.ts files two please.