Tip 46: Maintain State Over Time with LocalStorage

Preserving user data

Users love to personalize applications. Conversely, they hate entering the same data every time they visit an app or a page. When you’re working with front-end JavaScript, you’re in a bit of a bind. How do you preserve user data with minimal interference?

An obvious solution is to create a login. The problem is that many users will abandon a site if they’re forced to log in. A better, albeit imperfect, solution is to store data locally. When you save data locally, you can preserve information on a particular browser on a particular device.

Of course, everyone uses multiple devices. So saving data to a browser won’t help a user who works across multiple devices. Still, it’s far less intrusive than demanding a user make yet another account.

Using localStorge to store user data

You can easily save user information with localStorage. localStorage is like a tiny database that exists only in your browser. You can add and retrieve information from it, but it isn’t accessible by JavaScript in the browser.

Think back to your pet adoption site from Tip 13, Update Key-Value Data Clearly with Maps. You set up a series of filters to show only relevant pets. Because pet owners tend to prefer certain types of animals—lovers of labradors probably won’t look for tiny dogs—you could do them a favor if you save their searches between sessions.

Start by saving a breed preference. To save a breed, you just need to set the value on the localStorage object using the setItem() method. You pass the key as the first argument and the value as the second. The syntax should look familiar. It’s nearly identical to the method for setting data on a map.