How come this.__proto__ being deprecated but Object.getPrototypeOf(this) not implemented?

Code using deprecated __proto__ (see screenshot) works:

var Obj = function(val) {


  this.val = (val) ? val : this.__proto__.defaultVal;
};

Obj.prototype.defaultVal = "defaultVal";

Obj.prototype.getVal = function() {
  return this.val;
};

var objDefault = new Obj();

console.log("val = " + objDefault.getVal());

Console output:

 1v85 Copyright 2016 G.Williams
>echo(0);
val = defaultVal
=undefined
> 

Code 'correctly' getting prototype:

...
  this.val = (val) ? val : Object.getPrototypeOf(this).defaultVal; // line 4
...

Console output:

 1v85 Copyright 2016 G.Williams
>echo(0);
Uncaught Error: Function "getPrototypeOf" not found!
 at line 4 col 33
...val = (val) ? val : Object.getPrototypeOf(Obj).defaultVal;...
                              ^
in function "Obj" called from line 1 col 26
var objDefault = new Obj();
                         ^
val =
Uncaught Error: Field or method "getVal" does not already exist, and can't create it on undefined
 at line 1 col 34
console.log("val = " + objDefault.getVal());
                                 ^
=undefined
>

1 Attachment