Managing data in components.
WHAT STATE IS FOR
Data that changes and affects what is displayed.
WHAT NOT TO PUT IN STATE
Values derivable from other state Values that do not affect rendering
WHY
Derived state duplicates a source of truth, and the copies diverge.
WHAT TO DO INSTEAD
Compute it during rendering.
WHAT THE RULES OF HOOKS ARE
Call them at the top level of a component, never inside conditions or loops Call them only from components or other hooks
WHY
React identifies them by call order, and varying it breaks the association.
WHAT UPDATING STATE DOES
Schedules a re-render. It does not change the value immediately.
WHAT THAT CAUSES
Reading the value straight after setting it, and seeing the old one.
WHAT TO DO WHEN UPDATING BASED ON THE PREVIOUS VALUE
Use the function form, which receives the current value.
WHY
Several updates in one event otherwise operate on a stale value.
WHAT TO KEEP STATE AS
The minimum that describes the interface.
WHAT TO LIFT
State needed by several components, to their nearest common ancestor.
