localStorage is part of the [Web Storage API](https://developer.mozilla.org/en-US/docs/Web/API/Web_Storage_API) and provides a simple way to store key–value pairs directly in the browser. It allows web applications to save small amounts of data that persist even after the page is reloaded or the browser is closed. A particularly useful feature is the [`storage` event](https://developer.mozilla.org/en-US/docs/Web/API/Window/storage_event), which lets other open windows or tabs of the same origin react in real time when `localStorage` is updated. This makes `localStorage` a practical tool for syncing state between multiple browser windows or tabs.