IE doesn't understand ES6 (const, let and arrow functions are the ES6 things that I see in the package sources) and to provide IE compatibility (curse him) we need to have our vendor bundles in ES5. And it's not easy to transpile a specific library during bundling...

The common way is to have ./dist/compare-strings.js in the npm package repo and an npm build script for ES6 -> ES5 transpilation process. If it's ok, I can provide a PR covering this situation. What do you think?