localStorage With Expiry

Requirements

• Export ExpiringStorage as named and default. Constructor accepts optional storage and now function, defaulting to localStorage and Date.now. The adapter provides getItem, setItem, and removeItem.
• setItem(key, value, ttlMilliseconds) writes JSON.stringify({ value, expiresAt }), with expiresAt = now() + ttlMilliseconds. Values are JSON-serializable; undefined, functions, symbols, and unsupported nested values are outside scope.
• TTL must be finite and nonnegative, and the resulting expiry must be finite. Reject invalid values with RangeError before writing. TTL 0 is immediately expired.
• getItem(key) returns the parsed value before expiry. At now() >= expiresAt, delete the stored record and return null. A missing key returns null. Expiry is lazy; do not create timers.
• Malformed JSON or envelopes without an own value or finite numeric expiresAt must be deleted and return null. Preserve falsy stored values such as 0, false, and empty string. Stored null also returns null.
• removeItem(key) deletes that key. Rewriting a key replaces its value and expiry. Instances sharing an adapter read the same data. Propagate serialization and storage errors, including quota/access errors; do not clear unrelated keys.

Examples

Input: const cache = new ExpiringStorage();
cache.setItem("settings", { theme: "dark" }, 60000);
cache.getItem("settings");
Output: { theme: "dark" } before expiry, null at or after expiry.

Input: cache.setItem("count", 0, 1000);
cache.getItem("count");
Output: 0 before expiry.