“Uncaught ReferenceError: this is not defined” in class constructor

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This is a fact of the new class syntax. Your subclass needs to call super() in order for the class to be properly initialized, e.g.

super(arg1, arg2, argN);

with whatever arguments the parent constructor needs.

It is required that, if execution reaches the end of a constructor function, the value of this needs to have been initialized to something. You either need to be in a base class (where this is auto-initialized), have called super() so this is initialized, or returned an alternative object.

class Player extends Entity {
  constructor() {
    super();
    console.log("Created"); ;// error here
  }
}

You can think of it like constructor functions kind of have an automatic return this at the end of them.

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