Do these 3 things before closing this tab:
1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsWhen React state changes, React schedules the affected component to render again. The component runs with its updated state, React compares the new element tree with the previous one, and React commits the DOM changes it determines are needed. A render is not the same as recreating the entire DOM.
What happens after a state update?
- React schedules rendering. A state or props change can prompt React to render the component with its updated inputs.
- The component runs again. For a function component, React calls the component function, which produces a new description of the UI.
- React reconciles the result. It compares the new element tree with the previous result to determine what needs to change.
- React commits necessary DOM changes. React applies the changes it determines are needed; it does not automatically rebuild every DOM node just because a component rendered again.
For example, a counter might produce <button>0</button> before an update and <button>1</button> afterward. The component runs again to describe the updated UI, while React determines the DOM work required to reflect the new value.
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Does every re-render mean the whole page is rebuilt?
No. A re-render means React evaluated a component again and produced a new element tree. Reconciliation determines which updates are needed, and the commit applies the resulting DOM changes. The component function running again and every DOM node being recreated are different things.
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When should you worry about a re-render?
A re-render alone does not establish that there is a performance problem. The useful question is whether it caused unnecessary or expensive work. React DevTools Profiler can help identify where rendering work is occurring and whether it is costly.
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Should you optimize with memoization?
Understand and measure the work before reaching for useMemo, useCallback, or React.memo. These are possible optimization tools, not automatic requirements whenever a component renders again. As Alaa Samy puts it in “30 Days of Frontend – Day 1”, “Profile first. Optimize second.”
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