nixos-config/profiles/opencode/skill/vercel-react-best-practices/rules/rerender-memo-with-default-value.md

title, impact, impactDescription, tags

title	impact	impactDescription	tags
Extract Default Non-primitive Parameter Value from Memoized Component to Constant	MEDIUM	restores memoization by using a constant for default value	rerender, memo, optimization

Extract Default Non-primitive Parameter Value from Memoized Component to Constant

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().

To address this issue, extract the default value into a constant.

Incorrect (onClick has different values on every rerender):

const UserAvatar = memo(function UserAvatar({ onClick = () => {} }: { onClick?: () => void }) {
  // ...
})

// Used without optional onClick
<UserAvatar />

Correct (stable default value):

const NOOP = () => {};

const UserAvatar = memo(function UserAvatar({ onClick = NOOP }: { onClick?: () => void }) {
  // ...
})

// Used without optional onClick
<UserAvatar />