In this article Kent C. Dodds clearly explains what the downsides are of using Class in JavaScript.

Classes (and prototypes) have their place in JavaScript. But they’re an optimization. They don’t make your code simpler, they make it more complex. It’s better to narrow your focus on things that are not only simple to learn but simple to understand: functions and objects.

https://medium.com/@kentcdodds/classes-complexity-and-functional-programming-a8dd86903747