Interview Q&A / System Design
System Design interview questions
Caching, scaling, databases and classic design problems for beginners.
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- How do you focus an input automatically when a component mounts?
Attach a ref to the input with ref={inputRef}, then call inputRef.current.focus() inside a useEffect with an empty dependency array. The ref is filled only after the element is in the DOM.
BeginnerQuick answer1 min read - What does useRef return, and does changing ref.current cause a re-render?
It returns a mutable object { current } that stays the same across renders. Changing ref.current does not trigger a re-render, so refs suit values React does not need to display, such as timer IDs or DOM nodes.
BeginnerQuick answer1 min read