45 lines
1.0 KiB
Markdown
45 lines
1.0 KiB
Markdown
---
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title: Hoist callbacks to the root of lists
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impact: MEDIUM
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impactDescription: Fewer re-renders and faster lists
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tags: tag1, tag2
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---
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## List performance callbacks
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**Impact: HIGH (Fewer re-renders and faster lists)**
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When passing callback functions to list items, create a single instance of the
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callback at the root of the list. Items should then call it with a unique
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identifier.
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**Incorrect (creates a new callback on each render):**
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```typescript
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return (
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<LegendList
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renderItem={({ item }) => {
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// bad: creates a new callback on each render
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const onPress = () => handlePress(item.id)
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return <Item key={item.id} item={item} onPress={onPress} />
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}}
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/>
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)
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```
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**Correct (a single function instance passed to each item):**
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```typescript
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const onPress = useCallback(() => handlePress(item.id), [handlePress, item.id])
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return (
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<LegendList
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renderItem={({ item }) => (
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<Item key={item.id} item={item} onPress={onPress} />
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)}
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/>
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)
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```
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Reference: [Link to documentation or resource](https://example.com)
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