Nicholai
75168f7678
structure: state/CURRENT.md — 2-4 line session state (rewritten each session) events/ — json event bus (pull-based, optional context) persistent/ — important decisions (one doc per decision) emit — helper script for emitting events
39 lines
1.1 KiB
Markdown
39 lines
1.1 KiB
Markdown
---
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title: Extract Default Non-primitive Parameter Value from Memoized Component to Constant
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impact: MEDIUM
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impactDescription: restores memoization by using a constant for default value
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tags: rerender, memo, optimization
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---
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## Extract Default Non-primitive Parameter Value from Memoized Component to Constant
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When memoized component has a default value for some non-primitive optional parameter, such as an array, function, or object, calling the component without that parameter results in broken memoization. This is because new value instances are created on every rerender, and they do not pass strict equality comparison in `memo()`.
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To address this issue, extract the default value into a constant.
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**Incorrect (`onClick` has different values on every rerender):**
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```tsx
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const UserAvatar = memo(function UserAvatar({ onClick = () => {} }: { onClick?: () => void }) {
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// ...
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})
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// Used without optional onClick
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<UserAvatar />
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```
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**Correct (stable default value):**
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```tsx
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const NOOP = () => {};
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const UserAvatar = memo(function UserAvatar({ onClick = NOOP }: { onClick?: () => void }) {
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// ...
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})
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// Used without optional onClick
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<UserAvatar />
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```
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