Via LtU I read about a tail call optimization decorator. Of course I immediately wondered if it was possible in JavaScript, and it is:

Function.prototype.tailCallOptimized = function()
{
  var g = this;
  return function()
  {
    for (var caller = arguments.callee.caller; caller; caller = caller.caller)
      if (caller == arguments.callee)
        throw {tailCallArgs: arguments, tailCallThis: this};

    var args = arguments;
    var me   = this;
    while (true)
    {
      try
      {
        return g.apply(me, args);
      }
      catch(e)
      {
        if (!e.tailCallArgs)
          throw e;

        args = e.tailCallArgs;
        me   = e.tailCallThis;
      }
    }
  };
}

It improves somewhat on the Python example. It allows mutual recursion and recursive methods:

Number.prototype.isEven = function()
{
  return this == 0 ? true  : (this - 1).isOdd();
}
.tailCallOptimized();

Number.prototype.isOdd = function()
{
  return this == 0 ? false : (this - 1).isEven();
};

alert((10001).isEven() ? "even" : "odd");

Note the ‘decorator style’ in Javascript, simply a method call on the function.