What is the primary use of `localStorage` in JavaScript?

The primary use of localStorage in JavaScript is indeed to store key/value pairs without expiration. This mechanism allows for the persistent storage of data in a web browser, meaning that the data will remain until explicitly deleted by the user or through code, even when the browser is closed and reopened. This makes it suitable for saving user preferences, settings, or any data that needs to persist across sessions without a timeframe limit.

LocalStorage is part of the Web Storage API, which also includes sessionStorage. Unlike sessionStorage, data stored in localStorage does not get cleared when the session ends, making localStorage ideal for applications that require long-term storage.

The other options address different storage mechanisms or functionalities: temporary storage is handled by sessionStorage, which only retains data for the duration of the page session; session-specific variables are also tied to sessionStorage; and while localStorage can hold considerable amounts of data, it is not specifically designed for structured databases, as that would typically involve more complex storage solutions like IndexedDB.