panorix.app/preview · React fundamentals
React fundamentals
6 messages U
How does React decide when to re-render a component?
A
React re-renders a component when its state or props change. The reconciler diffs the previous virtual DOM tree against the new one, and only the changed nodes get updated in the actual DOM. Pure components and React.memo can short-circuit this when nothing meaningful changed.
U
What about useMemo for expensive computations?
A
useMemo caches the result of a computation across renders, recomputing only when its dependency array changes. Use it when the computation is genuinely expensive — for cheap calculations, the bookkeeping overhead can outweigh the savings.
U
When should I use useCallback vs useMemo?
A
useCallback memoizes a function reference; useMemo memoizes any value (including computed results). In practice, useCallback is just useMemo for functions. Reach for them when you're passing the value to a memoized child or when stable identity matters for an effect dependency.
Ask a follow-up…
懂延遲載入
現代應用常常邊瀏覽邊載入內容, Panorix 等每段載入完再截 —— 拼出來不會有空白行。
黏性頭尾只出現一次
聊天輸入框、固定頭部能被認出來, 只在截圖最頂部出現一次, 不會每一屏都重複。
內置 AI Reading 匯出
強烈建議長聊天截圖用上: 切片打包成 ZIP, 丟給 ChatGPT 或 Claude, 這次 AI 真能把整段對話讀完。