I'm looking for a library able to minify ES6 modules implementing clases with private members. All I have tried so far, including Google Closure Compiler, uglify-es, babel-minify, fails when they encounter #stage or any other member beginning with # (they explicitly complains about that character). For example this won't compile:

export default class QuiddisMakePlayer {

    #stage;
    #scormTracker;

    constructor(url, api){
        this.setup(url, api);
    }
   
    setup(){}

}