How to store value into sessionafter refresh the page?

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You cant' because Session is a Server object and javascript - purely a client side technology.
You need to work this at server side/code behind or use Ajax/web services to change the value..

Session data is saved on the server.  You can write all the client side Javascript you want, but it won't save anything on the server until you trigger a postback somehow.  You can either do AJAX or you can have some sort of control event that triggers a postback.  Somehow your client has to get the data to the server. 

In other words, just writing <% Session[x] = y; %> in a client side Javascript does nothing.  There's no postback, not contact with the server to tell it to update Session.