Comment by jeswin

Correct me if I'm wrong, but the necessity for decorators seem to have risen from the ES6 class syntax.

If we were doing classes/functions the old imperative style, we could have simply wrapped the RHS in a standard function that does what the decorator does.

  Animal.prototype.speedup = typeCheckDecorator("number", "number", function(x) {
    this.speed += x;
    return this.speed;
  });

I get that the class syntax makes things easier for people coming from other languages. And maybe makes static analysis easier. But still not sure if it was really needed.