javascript - Cannot define prototype properties within ES6 class definition

Question

I was trying ES6 syntax and find I cannot define prototype property or instance property within class defination, why forbids it?

I was using MyClass.prototype.prop=1 before, try ES7 by babel compiler as below, still cannot define prototype property.

class MyClass{
  prop=1;
  static sProp=1;
}

I don't think define instance property is any dangerous, there's 2 cases in my own browser game need prototype property:

1. Subclass instances need to inherit same property value from base class:

   var Building=function(){...}
   Building.prototype.sight=350;
   TerranBuilding.CommandCenter=...(CommandCenter extends Building)
   TerranBuilding.Barracks=...(Barracks extends Building)
   

So CommandCenter and Barracks will both have same building sight as 350.

new CommandCenter().sight===new Barracks().sight//All buildings have same sight

2. Buffer effect override original property and remove buffer
   

   Marine.prototype.speed=20
   var unit=new Marine()
   unit.speed===20//get unit.__proto__.speed 20
   unit.speed=5//Buffer:slow down speed, unit.speed will override unit.__proto__.speed
   delete unit.speed//Remove buffer
   unit.speed===20//true, speed restore
   

So I think it should add a way to set prototype property instead of forbid it completely, or can you give some other solutions to deal with above 2 cases?

Answer 1

Neither of those will be on the class prototype.

The class Foo { bar = 1; } syntax will assign a value to the class instance, to be accessed with this.bar.

The class Foo { static bar = 1; } syntax will assign a value to the class constructor, to be accessed with Foo.bar.

There isn't much reason to use the prototype in this case. It will only complicate who actually owns the property and assigning a number in a few different classes will have very little overhead.

I would suggest the class instance property and just use this.sight everywhere you need it.