Is HTML5 localStorage asynchronous?

html

async-programming

localstorage

javascript

byNikita Barsukov·Oct 10, 2024

Nope, localStorage ain't chillin' asynchronously. Functions like setItem and getItem take the stage immediately and put the rest of the JavaScript show on hold. Take a look:

// Synchronously storing data, because why delay gratification?
localStorage.setItem('key', 'value');

// Get that synchronously stored data—No need to handle suspense here!
var data = localStorage.getItem('key');

This behavior ensures all operations are as predictable as your favorite movie's plot twist.

How localStorage syncs up

To keep things fun, let's spill some beans on the synchronous nature of the localStorage API. When it comes to setItem and getItem, they'd rather hog the JavaScript limelight and hold up other operations than patiently wait their turn.

Event Loop and localStorage: Not best buddies

The JavaScript event loop does a fantastic job handling asynchronous operations without stopping the world. But localStorage likes to play by its own rules. It doesn't dance to the event loop's tune, preferring instead to operate in the NOW—putting subsequent performances on hold until it's done with its moment under the spotlight.

Performance: Don't take the "local" in localStorage lightly

localStorage.setItem doesn't wait for a disk write—it's not that patient! As a result, treating localStorage as a heavy-duty storage container can make your app as slow as a turtle trying to sprint.

localStorage: The rule-abider

When it comes to the localStorage spec, it's all about "must", "shall", and "may". These aren't just words—these are laws ensuring there's no ambiguity about localStorage's timing behavior.

HTML5 localStorage: A dash of history

You say "HTML5 localStorage"—we say "A bit of a history lesson!". While Web Storage (which includes localStorage) used to be part of the HTML5 specification, it isn't any longer. But, well, old habits die hard, don't they?

localStorage: Myths busted & tips shared

Let's get practical and address crucial elements of handling localStorage to save you hours of Googling (or Stack Overflow-ing).

localStorage: Not a Cinderella story

localStorage might remind you of Cinderella—it falls short when dealing with large volumes of data. For large datasets, IndexedDB is more of a fairy godmother solution—it's truly asynchronous and won't choke your UI.

Cross-tab chaos: Sorted

localStorage doesn't acknowledge browser tab boundaries. When multiple tabs access localStorage, it can turn into a game of tic-tac-toe where one tab nabs the spot another tab had its eyes on. Be a pro and use the storage event to keep peace across tabs.

Browser restrictions: Be prepared

Even localStorage has down days. Always plan for scenarios when localStorage throws a tantrum—private browsing mode, full storage quota, etc. A well-devised fallback strategy would be your insurance here.

Security: Not so secure

localStorage is like an open diary—it's highly accessible via JavaScript, and there's no encryption in place. So, keep "sensitive data" and localStorage away from each other to avoid a security breach fiasco.