1---
2title: Pass Primitives to List Items for Memoization
3impact: HIGH
4impactDescription: enables effective memo() comparison
5tags: lists, performance, memo, primitives
6---
7 
8## Pass Primitives to List Items for Memoization
9 
10When possible, pass only primitive values (strings, numbers, booleans) as props
11to list item components. Primitives enable shallow comparison in `memo()` to
12work correctly, skipping re-renders when values haven't changed.
13 
14**Incorrect (object prop requires deep comparison):**
15 
16```tsx
17type User = { id: string; name: string; email: string; avatar: string }
18 
19const UserRow = memo(function UserRow({ user }: { user: User }) {
20  // memo() compares user by reference, not value
21  // If parent creates new user object, this re-renders even if data is same
22  return <Text>{user.name}</Text>
23})
24 
25renderItem={({ item }) => <UserRow user={item} />}
26```
27 
28This can still be optimized, but it is harder to memoize properly.
29 
30**Correct (primitive props enable shallow comparison):**
31 
32```tsx
33const UserRow = memo(function UserRow({
34  id,
35  name,
36  email,
37}: {
38  id: string
39  name: string
40  email: string
41}) {
42  // memo() compares each primitive directly
43  // Re-renders only if id, name, or email actually changed
44  return <Text>{name}</Text>
45})
46 
47renderItem={({ item }) => (
48  <UserRow id={item.id} name={item.name} email={item.email} />
49)}
50```
51 
52**Pass only what you need:**
53 
54```tsx
55// Incorrect: passing entire item when you only need name
56<UserRow user={item} />
57 
58// Correct: pass only the fields the component uses
59<UserRow name={item.name} avatarUrl={item.avatar} />
60```
61 
62**For callbacks, hoist or use item ID:**
63 
64```tsx
65// Incorrect: inline function creates new reference
66<UserRow name={item.name} onPress={() => handlePress(item.id)} />
67 
68// Correct: pass ID, handle in child
69<UserRow id={item.id} name={item.name} />
70 
71const UserRow = memo(function UserRow({ id, name }: Props) {
72  const handlePress = useCallback(() => {
73    // use id here
74  }, [id])
75  return <Pressable onPress={handlePress}><Text>{name}</Text></Pressable>
76})
77```
78 
79Primitive props make memoization predictable and effective.
80 
81**Note:** If you have the React Compiler enabled, you do not need to use
82`memo()` or `useCallback()`, but the object references still apply.
83