Object.prototype woes

I’m having a problem creating some custom prototypes for the Flash Object. It’s supposed to link one variable to another, so when you modify x, y and z are automatically adjusted based on the value of x. It could be a very useful thing, and I’m trying to do it with the Object.watch property. The problem is that when everything has run the anchor value is removed from the object.

a = {x:0, y:1, z:0};
a.setLinked(“x”, [“y”, “z”], 0.5);
a.x = 10;

will set y and z to be 10*0.5, but the x value becomes blank. I’ve traced it right down to the end of the watch function and the x value is still at it’s original value, but as soon as everything is finished the x value is gone.

Anyone have any suggestions?
here’s the code and the FLA.

                   --=::Cheers ::=--
Object.prototype.setLinked = function (anchor, links, modifier)
 // abort the linking if required data is unspecified or the values to be linked do not exist
 if (anchor == undefined)
  return false;
 if (links == undefined)
  return false;
 if (eval("this." add anchor) == undefined)
  return false;
 if (modifier == undefined)
  modifier = 1;
 // create a link object based on the anchor
 set("link" add anchor, new Object());
 // create the linked array in the newly created link object
 eval("this.link" add anchor).linked = [];
 // if the links value is an Object
 if (links instanceof Object){
  // check all values of the links object to make sure they exist
  for (var i = 0; i< links.length; i++){
   if (eval("this." add links*) == undefined)
    return false;
  // copy the provided list into the object
  eval("this.link" add anchor).linked.duplicate(links);
 } else {
  // the links value is a variable, check if it exists
  if (eval("this." add links) == undefined)
   return false;
  // store the value in the first index of the array
  eval("this.link" add anchor).linked[0] = links;
 // store the link modifier value in the link object
 eval("this.link" add anchor).linkModifier = modifier;

 // check for the successful watching of the anchor object
 success = this.watch(anchor, function(id, oldval, newval){this.changeLinked(id, oldval, newval)});

 if (success)
  trace(links add " linked SUCCESSFULLY to " add anchor);
  trace("Linking FAILED");

 return success;

Object.prototype.changeLinked = function (id, oldval, newval)
 //  loop through the array of links and assign the newval value to all linked variables
 for (i in eval("this.link" add id).linked)
  if (isFinite(i))
   set("this." add eval("this.link" add id).linked*, newval*eval("this.link" add id).linkModifier);


// A prototype for copying objects without linking them
Object.prototype.duplicate = function (obj)
 for(var i in obj){

  if(obj* instanceof Array){
   this* = [];
  } else if (typeof obj* == "object"){
   this* = {};
  } else if(typeof obj* == "string" || typeof obj* == "number" || typeof obj* == "boolean" || obj* != null){
   this*= obj*;

// A prototype for copying arrays without linking them
Array.prototype.duplicate = function (arr)
 for (var i in arr){
  if(arr* instanceof Array){
   this* = [];
  } else if(typeof arr* == "string" || typeof arr* == "number" || typeof arr* == "boolean" || arr* != null){
   this*= arr*;