Rocket Loader is a general-purpose asynchronous JavaScript loader coupled with a lightweight virtual browser which can safely run any JavaScript code after window.onload.
Turning on Rocket Loader will immediately improve a web page’s window.onload time (assuming there is JavaScript on the page),
HI. thanks for your reply. i got it resolved. actually it was error caused when i forcefully deleted w3 cache plugin from ftp after a error. i reinstalled it and deleted all cache and it was gone.