mirror of
https://github.com/kjanat/livedash-node.git
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Kaj Kowalski
cd05fc8648
- Fix syntax errors in skills markdown files (.github/skills, .opencode/skills) - Change typescript to tsx for code blocks with JSX - Replace ellipsis (...) in array examples with valid syntax - Separate CSS from TypeScript into distinct code blocks - Convert JavaScript object examples to valid JSON in docs - Fix enum definitions with proper comma separation
69 lines
1.6 KiB
Markdown
69 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(document.cookie.split("; ").map((c) => c.split("=")));
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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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