Proper tail recursion in javascript

tail_recursion.js

// object containing the call and parameters, and optionally context
function tail_call() {
  this.params = Array.prototype.slice.call(arguments);
  this.fn = this.params.shift();
}
tail_call.prototype.self = function (context) {
  this.that = context;
  return this;
}

// wrapper that continually makes tail calls and returns final result
function tail_wrap(tc) {
  var x = tc;
  while (x instanceof tail_call) {
    var that = this;
    if (x.that != undefined) that = x.that;
    x = x.fn.apply(that, x.params);
  }
  return x;
}

// fibonacci
function fib_tail(n, f1, f2) {
  if (n == 0) {
    return f1;
  }
  console.log(n, f1, f2);
    // this is the way tail calls are performed. looks lispy now, doesn't it?
  return new tail_call(fib_tail, n - 1, f2, f1 + f2);
}

// and the wrapper
console.log(tail_wrap(fib_tail(10, 1, 1)));