Code Snippet of the Day — June 29, 2026

🌐 Code Snippet of the Day — June 29, 2026

LocalStorage with Automatic Expiration (TTL) — JavaScript

Vanilla localStorage never expires. This zero-dependency wrapper adds automatic TTL so stale data self-cleans. Perfect for API response caching, session tokens, and time-limited preferences.

const TTLStorage = (() => {
  const PREFIX = "ttl_";

  function set(key, value, ttlSec = 3600) {
    const wrapped = `${PREFIX}${key}:${ttlSec}`;
    localStorage.setItem(wrapped, JSON.stringify({
      value,
      expiresAt: Date.now() + ttlSec * 1000
    }));
  }

  function get(key) {
    for (let i = 0; i < localStorage.length; i++) {
      const k = localStorage.key(i);
      if (!k?.startsWith(`${PREFIX}${key}:`)) continue;
      const raw = localStorage.getItem(k);
      if (!raw) continue;
      let entry;
      try { entry = JSON.parse(raw); } catch { localStorage.removeItem(k); continue; }
      if (Date.now() > entry.expiresAt) { localStorage.removeItem(k); continue; }
      return entry.value;
    }
    return undefined;
  }

  function has(key) { return get(key) !== undefined; }

  function gc() {
    let cleaned = 0;
    for (let i = 0; i < localStorage.length; i++) {
      const k = localStorage.key(i);
      if (!k?.startsWith(PREFIX)) continue;
      const raw = localStorage.getItem(k);
      try {
        const entry = JSON.parse(raw);
        if (Date.now() > entry.expiresAt) { localStorage.removeItem(k); cleaned++; }
      } catch { localStorage.removeItem(k); cleaned++; }
    }
    return cleaned;
  }

  return { set, get, has, gc };
})();

// Usage:
TTLStorage.set("userProfile", { name: "Alice" }, 300);  // 5 min TTL
const profile = TTLStorage.get("userProfile");            // undefined if expired
const cleaned = TTLStorage.gc();                          // clean all expired

💡 Every frontend project needs expiring storage — this is the simplest implementation that actually works.