yc.js

var factorial = function(self) {
  return function(x) {
    if(x < 1){
      return 1;
    }else{
      return x * self(x - 1);
    }
  }
};


var yc = function(rfn) {
  return function(x) {
    var o = function(y) {
      var result = rfn(o)(y);
      if (result == NaN) {
        return rfn(rfn(o));
      }else{
        return result;
      }
    };
    return rfn(o)(x);
  }
};

yc(factorial)(5);
// 120