Thank you F1Fan for your reply.
I got the idea that you meant by the code snippets. But I am a little confused that from where the getURLString() and checkForURLUpdates() functions call from? Here you mention about only one function, checkForFeatureActionUpdates() for repetative call. In my javascript page I have defined a number of functions like drafts(src,mail_id,to,subj,mes), uploading(src,attach). How that is possible? How we can call different functions on browser back button click? How can we define checkForFeatureActionUpdates() function?