What is the best way to store variable using js for its later usage?

Question

I have created a billing program in which i want the total of every bill to be added to the next total and this should get saved in a variable and when i close the window or refresh it, the variable should retain the previous totals.

Answer 1

by closing/refreshing the window you loose all data that wasn't saved on a database, in a file on the server, in local storage or cockies.
Unless you go for options like these you won't be able to retreive data after a window is closed.