Uncaught TypeError when used in 'use strict' mode

Very nice app! It works really well when I reference the file as instructed.

I thought it would be nice to use it as a module but ran into issues when doing so. I think it's because ES6 javascript modules enforce strict mode.

When imported with import './code-128-encoder.min.js'; I get this error code-128-encoder.min.js:3 Uncaught TypeError: Cannot use 'in' operator to search for 'String' in undefined at Object.$jscomp.polyfill.