private fields, getter/setter in JS

privateFields.js

function MyClass( paramA ){
   propertyR = "this property is read-only";
   
   this.getPropertyR = function(){
      return propertyR;
   };
   
   function privateMethod() {
      return "privateMethod() is a private method";
   }
   
   propertyRW = paramA;
   this.getPropertyRW = function() {
      return propertyRW;
   };
   this.setPropertyRW = function( param ){
      propertyRW = param;
   };
   
   this.doSomeAction = function() {
      alert ( privateMethod() + " / " + this.getPropertyR() );
   };
}

alert( "var obj = new MyClass( 'A' );");
var obj = new MyClass( "A" );

alert( "alert ( obj.getPropertyR() );" );
alert ( obj.getPropertyR() );

alert( "obj.propertyR = 'write it!';" );
obj.propertyR = "write it!";

alert( "alert( obj.getPropertyRW() );" );
alert( obj.getPropertyRW() );

alert( "obj.setPropertyRW('oh yes, write me!');" );
obj.setPropertyRW("oh yes, write me!");

alert( "obj.getPropertyRW();" );
alert( obj.getPropertyRW() );

alert( "obj.doSomeAction();" );
obj.doSomeAction();

alert( "obj.privateMethod();" );
obj.privateMethod();

alert( "That's it, check the error console. There should be two errors for trying to access objectR and privateMethod" );