c86c93582e
- Add 8 new skills (62 total, up from 58) - Official Anthropic skills: docx, pdf, pptx, xlsx, brand-guidelines, internal-comms - Vercel Labs skills: react-best-practices, web-design-guidelines - Implement dual-versioning: -official/-anthropic and -community suffixes - Update README with new skill registry and credits - Regenerate skills_index.json (62 skills validated) - Add comprehensive walkthrough.md BREAKING CHANGE: Document skills (docx/pdf/pptx/xlsx) renamed with version suffixes
71 lines
1.6 KiB
Markdown
71 lines
1.6 KiB
Markdown
---
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title: Cache Storage API Calls
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impact: LOW-MEDIUM
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impactDescription: reduces expensive I/O
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tags: javascript, localStorage, storage, caching, performance
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---
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## Cache Storage API Calls
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`localStorage`, `sessionStorage`, and `document.cookie` are synchronous and expensive. Cache reads in memory.
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**Incorrect (reads storage on every call):**
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```typescript
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function getTheme() {
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return localStorage.getItem('theme') ?? 'light'
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}
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// Called 10 times = 10 storage reads
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```
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**Correct (Map cache):**
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```typescript
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const storageCache = new Map<string, string | null>()
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function getLocalStorage(key: string) {
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if (!storageCache.has(key)) {
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storageCache.set(key, localStorage.getItem(key))
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}
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return storageCache.get(key)
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}
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function setLocalStorage(key: string, value: string) {
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localStorage.setItem(key, value)
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storageCache.set(key, value) // keep cache in sync
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}
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```
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Use a Map (not a hook) so it works everywhere: utilities, event handlers, not just React components.
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**Cookie caching:**
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```typescript
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let cookieCache: Record<string, string> | null = null
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function getCookie(name: string) {
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if (!cookieCache) {
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cookieCache = Object.fromEntries(
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document.cookie.split('; ').map(c => c.split('='))
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)
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}
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return cookieCache[name]
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}
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```
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**Important (invalidate on external changes):**
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If storage can change externally (another tab, server-set cookies), invalidate cache:
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```typescript
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window.addEventListener('storage', (e) => {
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if (e.key) storageCache.delete(e.key)
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})
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document.addEventListener('visibilitychange', () => {
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if (document.visibilityState === 'visible') {
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storageCache.clear()
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}
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})
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```
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