Tail Call Optimization on the fly for tail recursive functions in Javascript (naive implementation)

tco.js

function range(s, e, res) {
  if (!res) { res = []; }
  res.push(s);
  if (s == e ) {
    return res;
  }
  else { 
    if (s<e) { s++; }
    else { s--; }
    return range(s, e, res);
  }
}


function tco(f) {
  var fs = f.toString(),
      fsmatch = fs.match(/function\s*([^()]*)\(([^)]*)\)/),
      fn = {},
      recurRx, modfn, modargs, _f, _fbody;

  // function 'f' must have a name to be recursive
  if (fsmatch.length >= 3) {
    // gather function information
    fn.name = fsmatch[1];
    fn.args = fsmatch[2].split(/\s*,\s*/);
    fn.arity = fn.args.length;
    fn.body = fs.substring(fs.indexOf('{') + 1, fs.lastIndexOf('}'));

    // find occurences of self calls, replace with loop continuation
    recurRx = new RegExp('((^\\s*)return\\s*'+fn.name.trim()+'\\s*\\([^)]*\\);?)', 'mg');
    modfn = fn.body.replace(recurRx, '$2_cont = true;\n$2continue _recur;');

    // Build the new, optimized function
    _fbody = [
      'var _cont = true;',
      '_recur: while (_cont) {',
      '  _cont = false;',
      modfn,
      '}'].join('\n');

    fn.args.unshift(null);

    _f = (new (Function.prototype.bind.apply(Function, fn.args.concat(_fbody))));
    return _f;
  }
  else {
    throw new Error("Unable to transpile function: ", f.toString());
  }
}

var _tco = tco(range);
console.log(_tco.toString());
_tco(1,32768);