node.js and generating modules at/during runtime

I'm currently working on a node.js project that requires generating and altering objects in memory at and during runtime. I know this sounds confusing, so here's an example.

Monday 10am:

var PI = Math.PI;

exports.area = function (r) {
   return PI * r * r;
};

Monday 11am:

var PI = Math.PI;
var minSize = 10;

exports.area = function (r) {
   if (r >= minSize) {
      return PI * r * r;
   } else {
      return "Error: Minimum size not met.";
   }
};

Monday 12noon:

var PI = Math.PI;
var minSize = 10;
var msg = "Error: Minimum size of " + minSize + "not met.";    

exports.area = function (r) {
   if (r >= minSize) {
      return PI * r * r;
   } else {
      return msg;
   }
};

Tuesday 10am:

var PI = Math.PI;
var minSize = 15;
var error['eng'] = "Error: Minimum size of " + minSize + "not met.";    
var error['chn'] = "錯誤：不符合最小尺寸:" + minSize + "。"    

exports.area = function (r) {
   if (r >= minSize) {
      return PI * r * r;
   } else {
      return error;
   }
};

exports.circumference = function (r) {
   if (r >= minSize) {
      return 2 * PI * r;
   } else {
      return error;
   }
};

This is a bit of a contrived example, because most of the changes could avoided with proper planning, I know, but it sort of goes to illustrate the point. This module kept changing in both variables and functions, expanding while the server is running.

Here are the restrictions I have:

• Use Prototypal Inheritance (no keyword "new")
• Changes take effect at the next call of the function
• Changes include addition of new variables and functions
• Changes need to be saved for server restarts
• Cannot use eval()

I've thought of two possible strategies:

1. Using .prototype, continue to add/change functions and variables.

   • Pros: Able to do it as the server is running
   • Cons: I'm not sure how to save it to file. As far as I know, I cannot save functions to file without using eval() in some way

2. Editing the files directly and reloading them through something like node-supervisor.

   • Pros: Changes would be saved over, versions could be saved and reverted back to
   • Cons: I think editing the files directly would more or less have the same consequence using eval(), ie, if someone sneaks something malicious the system could break.

That's all I can think of right now. Would appreciate any opinions or options in this area.