First: JS has no OOP. There is OLOO. The class keyword brings only syntactic sugar.
At the time of this writing, there are limited options for defining methods and properties with the class keyword. If you want to have modification save or non-enumerable methods and properties you have to define them after declaring your "class".
In example:
class Car {
//...
}
// Add a property
Car.prototype.color = 'white'
// Add a modification protected property
Object.defineProperty(Car.prototype, 'wheels', {
configurable: false, // defaut: false
enumerable: true, // default: false
writable: false, // default: false
value: 4
})
Same for statics.