is prototype able to reference 'this' ?

isPrototypeAbleToReferenceThisKeyword.js

function obj1(){
   this.param1 = 1;
   this.param2 = 2;
}

obj1.prototype.ProtoMethod = function(){
   this.param1 = 11;
   this.param2 = 22;
}

var obj = new obj1();
var befor1 = obj.param1;
var befor2 = obj.param2;

obj.ProtoMethod();   // <--

var after1 = obj.param1;
var after2 = obj.param2;

document.getElementById('test').innerHTML =
    "<br>  befor1:"+befor1 +
    "<br>  befor2:"+befor2+
    "<br>  after1:"+after1+
    "<br>  after2:"+after2
        ;