There are, however, situations where your application needs to transmit information to the server, for example, when the player hits a high score. What should you do if the game is running in offline mode at this moment?
The solution is to use web storage. We won't go into the details of all that you can do with web storage, but the basic idea here is to store all the information you want to send to the server in local storage and transmit it once the game is online again. This technology is part of the HTML5 specification and therefore supported only by modern browsers. The available space you have to save your data in is 5 MB, so you will have to use it wisely.
To store any value you want on the client's side, you can simply use the setItem method of the sessionStorage object. To retrieve the value, you can use the getItem method.
The following code shows exactly this:
sessionStorage.setItem('key','value');
sessionStorage.getItem('key');