useLayoutEffect

As explained in React Quickly, Second Edition

useLayoutEffect is a React Hook that runs an effect synchronously after a component renders into the DOM but before the browser paints the update.

useLayoutEffect is a specialized effect Hook for work that must happen immediately after React updates the DOM but before the browser displays the update. It can prevent users from seeing an incorrect intermediate UI, such as a temporary 0 before a letter count appears. section 6.1.6

Preventing a visible intermediate value

Replace useEffect with useLayoutEffect when an effect updates state and the first rendered value would otherwise briefly appear on screen. The layout effect runs immediately, React applies the resulting state update, and the browser displays the corrected UI first. Keep useEffect as the default; useLayoutEffect is for specialized timing-sensitive cases. section 6.1.6

Treat useLayoutEffect as useEffect with different timing:

• Pass an effect function and a dependency array. section 6.1.6
• When a dependency changes, run the previous cleanup, then run the new effect. section 6.1.6
• Use it only when asynchronous useEffect timing produces a visible or otherwise incorrect result. section 6.1.6

Figure 6.13 The timing of useLayoutEffect versus useEffect. Note how the layout effect is run just after the DOM is updated, but before the browser has had a chance to lay out the elements using CSS. (Sorry for the crowded diagram!)

Compare the execution points of useLayoutEffect and useEffect: the layout effect runs after the DOM update but before the browser lays out elements with CSS. section 6.1.6

How React Quickly, Second Edition covers it

How deep it goes

Explains timing, dependencies, cleanup, and rerender behavior, while stopping short of broader implementation internals.

Examples

Uses a letter-count display, a temporary zero, lifecycle-method conversion, and effect-timing diagrams.

What it assumes

Assumes familiarity with component rendering, state updates, useEffect, dependency arrays, and cleanup functions.

What you can do after

Apply it via React when useEffect allows a visibly incorrect intermediate render.

How it connects

Contrasts useEffect, updates state, operates after DOM rendering, and supports cleanup functions.

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Related concepts

• useEffectalternative to · useEffect is a React Hook that runs effect logic after rendering to synchronize a component with external systems and optionally perform cleanup.
• dependency arrayused by · A dependency array is an array passed to a React effect or memoization Hook that specifies values whose changes trigger recomputation or rerunning.
• resource cleanupuses · Resource cleanup is the release of resources or restoration of state when an operation or scope ends or fails.

This explainer was generated by Manning's knowledge graph from the text of React Quickly, Second Edition. The section links point to the parts of the book it draws on.