Cursor rule

1---
2alwaysApply: false
3---
4 
5## Extract Default Non-primitive Parameter Value from Memoized Component to Constant
6 
7When 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()`.
8 
9To address this issue, extract the default value into a constant.
10 
11**Incorrect (`onClick` has different values on every rerender):**
12 
13```tsx
14const UserAvatar = memo(function UserAvatar({ onClick = () => {} }: { onClick?: () => void }) {
15  // ...
16})
17 
18// Used without optional onClick
19<UserAvatar />
20```
21 
22**Correct (stable default value):**
23 
24```tsx
25const NOOP = () => {};
26 
27const UserAvatar = memo(function UserAvatar({ onClick = NOOP }: { onClick?: () => void }) {
28  // ...
29})
30 
31// Used without optional onClick
32<UserAvatar />
33```
34