Not mutable, but tethered state, I think OO&#x2F;Objects&#x2F;Classes work slightly better when used as a means of tethering state&#x2F;presentation&#x2F;events... not that they need to mutate... for example the React.Component via ES6-style classes doesn&#x27;t bug me as much as some... but I use it sparingly, most of the rest is more functional.