React
- useState
- useEffect
- perform “side effects” in functional components - which do things beyond the component’s direct rendering, like
- data fetching, API calls
- DOM manipulation
- subscribing to external events
- timers
- cleanup - removing event listeners, etc.
- Runs after every render by default
- useRef
- Persists mutable values across component renders without causing re-renders when the value changes
- returns a mutable ref object, whose
.current is the arg passed to useRef
- ideal for storing values that don’t affect visual output, but need to be maintained, such as
- prev state vals
- DOM references
- Timer Ids
- commonly used to get direct ref to a DOM element. use cases could be
- playing or pausing media
- focusing an input field
- measuring element dimensions