1---
2title: Version and Minimize localStorage Data
3impact: MEDIUM
4impactDescription: prevents schema conflicts, reduces storage size
5tags: client, localStorage, storage, versioning, data-minimization
6---
7 
8## Version and Minimize localStorage Data
9 
10Add version prefix to keys and store only needed fields. Prevents schema conflicts and accidental storage of sensitive data.
11 
12**Incorrect:**
13 
14```typescript
15// No version, stores everything, no error handling
16localStorage.setItem('userConfig', JSON.stringify(fullUserObject))
17const data = localStorage.getItem('userConfig')
18```
19 
20**Correct:**
21 
22```typescript
23const VERSION = 'v2'
24 
25function saveConfig(config: { theme: string; language: string }) {
26  try {
27    localStorage.setItem(`userConfig:${VERSION}`, JSON.stringify(config))
28  } catch {
29    // Throws in incognito/private browsing, quota exceeded, or disabled
30  }
31}
32 
33function loadConfig() {
34  try {
35    const data = localStorage.getItem(`userConfig:${VERSION}`)
36    return data ? JSON.parse(data) : null
37  } catch {
38    return null
39  }
40}
41 
42// Migration from v1 to v2
43function migrate() {
44  try {
45    const v1 = localStorage.getItem('userConfig:v1')
46    if (v1) {
47      const old = JSON.parse(v1)
48      saveConfig({ theme: old.darkMode ? 'dark' : 'light', language: old.lang })
49      localStorage.removeItem('userConfig:v1')
50    }
51  } catch {}
52}
53```
54 
55**Store minimal fields from server responses:**
56 
57```typescript
58// User object has 20+ fields, only store what UI needs
59function cachePrefs(user: FullUser) {
60  try {
61    localStorage.setItem('prefs:v1', JSON.stringify({
62      theme: user.preferences.theme,
63      notifications: user.preferences.notifications
64    }))
65  } catch {}
66}
67```
68 
69**Always wrap in try-catch:** `getItem()` and `setItem()` throw in incognito/private browsing (Safari, Firefox), when quota exceeded, or when disabled.
70 
71**Benefits:** Schema evolution via versioning, reduced storage size, prevents storing tokens/PII/internal flags.
72