I am trying to get a Javascript object to use the "this" assignments of another objects' constructor, as well as assume all that objects' prototype functions. Here's an example of what I'm attempting to accomplish:

 /* The base - contains assignments to 'this', and prototype functions
  */
 function ObjX(a,b) {
     this.$a = a,
          $b = b;
 }

 ObjX.prototype.getB() {
     return this.$b;
 }

 function ObjY(a,b,c) {
    // here's what I'm thinking should work:
    this = ObjX(a, b * 12); 
    /* and by 'work' I mean ObjY should have the following properties:
     * ObjY.$a == a, ObjY.$b == b * 12,
     * and ObjY.getB() == ObjX.prototype.getB()
     * ... unfortunately I get the error: 
     *     Uncaught ReferenceError: Invalid left-hand side in assignment
     */

    this.$c = c; // just to further distinguish ObjY from ObjX.
 }

I'd be grateful for your thoughts on how to have ObjY subsume ObjX's assignments to 'this' (i.e. not have to repeat all the this.$* = * assignments in ObjY's constructor) and have ObjY assume ObjX.prototype.

My first thought is to try the following:

function ObjY(a,b,c) {
   this.prototype = new ObjX(a,b*12);
}

Ideally I'd like to learn how to do this in a prototypal way (i.e. not have to use any of those 'classic' OOP substitutes like Base2).

It may be noteworthy that ObjY will be anonymous (e.g. factory['ObjX'] = function(a,b,c) { this = ObjX(a,b*12); ... }) -- if I've the terminology right.

Thank you.