$ snippet localstorage-with-expiry

localStorage with expiry and JSON

A tiny wrapper that stores objects, expires them after a TTL, and doesn't crash in private browsing or when the quota is full.

JavaScript

const store = {
  /** store.set("session", { id: 1 }, 60 * 60 * 1000) — expires in 1 hour (omit ttl for no expiry) */
  set(key, value, ttlMs) {
    const record = { value, expires: ttlMs ? Date.now() + ttlMs : null };
    try { localStorage.setItem(key, JSON.stringify(record)); return true; }
    catch { return false; }            // quota exceeded, private mode, or storage disabled
  },
  get(key, fallback = null) {
    try {
      const raw = localStorage.getItem(key);
      if (raw === null) return fallback;
      const { value, expires } = JSON.parse(raw);
      if (expires && Date.now() > expires) { localStorage.removeItem(key); return fallback; }
      return value;
    } catch { return fallback; }       // corrupt JSON or storage unavailable
  },
  remove(key) { try { localStorage.removeItem(key); } catch {} },
};

How it works

Raw localStorage only stores strings, never expires anything, and throws in several real situations — Safari private mode in older versions, a full quota, or a browser setting that blocks storage. Wrapping every call in try and returning a fallback keeps the page working when storage doesn't. The expiry is checked lazily on read, which is enough for caches and "don't show this again for a week" flags.

Gotchas

Storage is per origin and synchronous; large values (hundreds of KB) block the main thread. For big or structured data use IndexedDB.
Never store secrets or tokens you would not want any script on the page to read — localStorage is fully exposed to XSS.
JSON.stringify drops undefined, functions and Date objects (dates become strings). Store timestamps as numbers.

Try it

Result

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