ClientState

Clientstate refers to data and UI state that resides on the client side, typically in a web browser, rather than on a server. It covers transient UI state (which component is visible), user preferences, draft form data, and cached data needed for rendering. Distinguishing client state from server state clarifies data authority: server state is the source of truth for business data, while client state is influenced by the user and the local environment and may be lost if the session ends.

Storage and persistence: In browsers, common mechanisms are in-memory variables, localStorage, sessionStorage, cookies, and IndexedDB. LocalStorage persists across sessions; sessionStorage lasts for a tab. Cookies can be sent with requests and have size limits. IndexedDB supports larger, structured data. Service workers and the Cache API can store assets and responses for offline use.

Management: In single-page applications, client state is often managed with a central store and actions or mutations that update state and trigger UI updates. Popular patterns include Redux, Vuex, MobX, NgRx, or framework-native solutions. State is typically kept as a single source of truth on the client and synchronized with server state as needed.

Security and reliability: Because client state can be modified by users, servers should validate all critical operations and not trust client state for authorization or integrity. Avoid storing sensitive credentials in localStorage or cookies; use short-lived tokens, HttpOnly cookies, and server-side validation.

See also: server state, web storage APIs, offline web applications.