React statebeginner
State is the data that changes while the page is open; useState is how a component remembers something between renders.
Shared cart state for the whole app, with no Redux and no Zustand. Context and a reducer, state nobody outside can mutate, an update that happens before the request and rolls back to the exact snapshot if it fails.
See alsoA Signal StoreThe same store in Angular: read-only state, an optimistic write and a rollback.
The cart is shared, the UI responds before the network does, and a failed request leaves the state exactly as it was.
Published in full, before you start — every point is one of these and there is nothing else.
State is the data that changes while the page is open; useState is how a component remembers something between renders.
A class with public setters on everything cannot stop anyone putting it in an impossible state; moving the mutation behind a named method is how the rule becomes unbreakable.
Anything that talks to a network can be slow or fail; a screen with no loading state and no error state is a screen that looks broken the first time the wifi drops.
Network calls fail. Code that assumes they succeed turns a slow connection into a blank screen with no explanation.
sort() and reverse() change the array you gave them, which is how a filter quietly reorders the caller's data — copy first, and the bug never exists.