Learn Ruby on Rails Book

Local storage and Session storage

For the longest time cookies were the only way to maintain state. Then HTML5 came. HTML5 provides two more ways of storing data on the browser - localStorage and sessionStorage.

Local storage

LocalStorage stores the data with no expiration date. It means the data will not be deleted when the browser is closed, and the data will be available the next day, next week, or even next year.

In chrome browser we can see the contents of localStorage by opening Developer tools > Application > Local Storage.

Setting, retrieving and deleting data from localStorage is pretty easy.

1localStorage.setItem("favoriteColor", "black");
2localStorage.favoriteColor;
3localStorage.removeItem("favoriteColor");

Local storage provides at least 5MB of data storage across all major web browsers. This a lot more than the 4KB (maximum size) that we can store in cookies.

LocalStorage data can be read by any JavaScript code. If a hacker is able to execute JavaScript code on our web application then the hacker will be able to steal all the data stored in the localStorage.

Session storage

Data stored in sessionStorage gets cleared when the page session ends. A page session lasts for as long as the browser is open and survives over page reloads and restores. Closing a tab/window ends the session and clears objects in sessionStorage.

1// Save data to sessionStorage
2sessionStorage.setItem("key", "value");
3
4// Get saved data from sessionStorage
5let data = sessionStorage.getItem("key");
6
7// Remove saved data from sessionStorage
8sessionStorage.removeItem("key");
9
10// Remove all saved data from sessionStorage
11sessionStorage.clear();

There is nothing to commit in this chapter since all we had done was learning the basics of localStorage and sessionStorage.

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