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405Rendering vs Committing: The Two-Phase Process
406What Happens During the Render Phase
407Pure Functions: Why Components Must Be Pure
408The Virtual DOM (Reconciliation)
409Fiber: React's Internal Reconciliation Engine
410When Components Re-render: The Trigger Rules
411Render Does Not Mean DOM Update
412The Commit Phase: Applying Changes to the DOM
413Strict Mode's Double-Render Behavior
414Console Logs and Render Counting
415Why Renders Are Usually Fast
416Visualizing Renders with React DevTools Profiler
417What is Batching and Why It Matters
418Automatic Batching in Event Handlers
419React 18's Automatic Batching Everywhere
420Batching Example: Multiple setState Calls
421Pre-React 18 Batching Limitations
422Observing Batching with Console Logs
423Batching Across Components
424When Batching Doesn't Apply
425The Performance Win from Batching
426Debugging: Expecting Multiple Renders
427The Three Phases of React Updates
428Render Phase: Pure Calculation
429Commit Phase: Applying Changes to the DOM
430Effects Phase: Running Side Effects After Paint
431Why Effects Can't Run During Render
432useLayoutEffect: Pre-Paint Synchronous Effects
433The Render-Commit-Effect Timeline Visualized
434Why State Updates Don't Appear Immediately
435Debugging with Phase Awareness
436State Updates Are Scheduled, Not Immediate
437Reading State Right After Setting It
438The Render Cycle Timeline
439Batching Hides Individual Updates
440Closures Capture State Snapshots
441Async Functions and Stale State
442Using Functional Updates to Avoid Staleness
443Why React Doesn't Offer Synchronous setState
444What flushSync Does: Breaking Out of Batching
445The flushSync Syntax and Import
446When You Actually Need flushSync
447The Performance Cost of flushSync
448flushSync with DOM Measurements
449Alternatives to flushSync: Effect-Based Solutions

405Rendering vs Committing: The Two-Phase Process
406What Happens During the Render Phase
407Pure Functions: Why Components Must Be Pure
408The Virtual DOM (Reconciliation)
409Fiber: React's Internal Reconciliation Engine
410When Components Re-render: The Trigger Rules
411Render Does Not Mean DOM Update
412The Commit Phase: Applying Changes to the DOM
413Strict Mode's Double-Render Behavior
414Console Logs and Render Counting
415Why Renders Are Usually Fast
416Visualizing Renders with React DevTools Profiler
417What is Batching and Why It Matters
418Automatic Batching in Event Handlers
419React 18's Automatic Batching Everywhere
420Batching Example: Multiple setState Calls
421Pre-React 18 Batching Limitations
422Observing Batching with Console Logs
423Batching Across Components
424When Batching Doesn't Apply
425The Performance Win from Batching
426Debugging: Expecting Multiple Renders
427The Three Phases of React Updates
428Render Phase: Pure Calculation
429Commit Phase: Applying Changes to the DOM
430Effects Phase: Running Side Effects After Paint
431Why Effects Can't Run During Render
432useLayoutEffect: Pre-Paint Synchronous Effects
433The Render-Commit-Effect Timeline Visualized
434Why State Updates Don't Appear Immediately
435Debugging with Phase Awareness
436State Updates Are Scheduled, Not Immediate
437Reading State Right After Setting It
438The Render Cycle Timeline
439Batching Hides Individual Updates
440Closures Capture State Snapshots
441Async Functions and Stale State
442Using Functional Updates to Avoid Staleness
443Why React Doesn't Offer Synchronous setState
444What flushSync Does: Breaking Out of Batching
445The flushSync Syntax and Import
446When You Actually Need flushSync
447The Performance Cost of flushSync
448flushSync with DOM Measurements
449Alternatives to flushSync: Effect-Based Solutions

Lesson 446 of 2,396·12. Rendering and BatchingPro lesson

When You Actually Need flushSync

Identify rare scenarios like measuring DOM after state changes or integrating with third-party libraries that require synchronous updates.

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