Local Storage vs. Session Storage vs. Cookies

When I needed to save a user's theme preference (dark mode) on my first web app, I was confused by the options. Cookies are the old school way. They are sent to the server with every HTTP request, which can slow things down, but they are necessary for authentication sessions. Local Storage and Session Storage, part of the Web Storage API, stay on the client side. Local Storage persists forever (until cleared manually), making it perfect for user settings. Session Storage lasts only for the current browser tab session; close the tab, and it's gone. The API is simple: localStorage.setItem('theme', 'dark') and localStorage.getItem('theme'). However, a key limitation is that they only store strings. So for objects, you need to use JSON.stringify() to save and JSON.parse() to retrieve. I once spent an hour debugging because I forgot to parse the object back, and I was getting '[object Object]' instead of my data.