Please rewrite this on ES6 and remove require of assert in the production build

[talamaska]

I do realise that this library was created long ago when js didn't had classes but now it is different. The require of assert is really another specific issue for using the library in electron. It is recommended to have nodeIntegration turned off, this means that any require will not work, but if it is import, that'ss another story and might just work. And last time I used assert was for tests or otherthings done only in dev build, not in production.