call JS object as a function

call-as-function.js

function Register(id, index)
{
  if (this instanceof Register) {
    this.index = index;
    this.id = id;
  }
  else {
    var self = new Register(id, index);
    var reg = self.funcall.bind(self);
    reg.__proto__ = self;
    reg.index = index;
    reg.id = id;
    return reg;
  }
}
Register.prototype = new Function;

Register.prototype.funcall = function(reg, disp) {
  return this;
};

var assert = require('assert');
var eax = Register('eax', 0);
assert(eax instanceof Register);
assert(eax instanceof Function);
assert(eax() !== eax); // === self, not reg :(
assert(eax.id === 'eax');
assert(eax.name === '');