We’ve all been there: You're building a web app, and you need to store a piece of data. Maybe it’s a user’s preferred theme, a half-filled form, or an authentication token. You know it belongs in the browser, but then the inevitable choice hits you:
Do I drop this in LocalStorage, stash it in SessionStorage, or bake a cookie?
It’s easy to treat these three as interchangeable buckets of data, but picking the wrong one can lead to broken user experiences, sluggish performance, or worse—gaping security holes.
Let’s break down how these browser storage mechanisms actually work under the hood, when to use them, and the architectural trade-offs you need to consider.
1. LocalStorage: The Long-Term Vault
