Cookie Store API maxAge attribute

concepts

1. maxAge Demo

   Set cookies with maxAge values (short-lived session, hourly, daily, weekly) and read them back immediately. The Cookie Store API returns a expires timestamp — confirm the maxAge maps correctly.

2. expires vs maxAge Comparison

   Side-by-side comparison of the old expires: new Date(Date.now() + duration) pattern versus the new maxAge: seconds shorthand. Shows why relative duration is more robust than absolute timestamps.

3. Session Rotator

   Rolling-session simulator with a live countdown meter — set, touch, or let the cookie expire. Subscribes to cookieStore.change events so you can see the lifecycle as it happens.

4. Cookie Manager

   A live cookie manager panel built entirely on the Cookie Store API. Set cookies with a maxAge slider, see all stored cookies with expiry bars, and watch cookieStore.change events fire in real time when cookies are created or deleted.

why it shipped

The Cookie Store API (cookieStore.set(), cookieStore.get()) was designed as a Promise-based replacement for the legacy document.cookie string. The classic document.cookie format supports Max-Age=N for relative expiry — far more reliable than Expires=date which depends on client clock accuracy. The Cookie Store API initially omitted maxAge, forcing developers to compute new Date(Date.now() + N * 1000) manually and pass it as expires. Chrome 145 adds the maxAge option so both absolute (expires) and relative (maxAge) lifetimes are available in the modern API.

the API

// Before Chrome 145 — had to compute absolute expiry
await cookieStore.set({
  name: 'session',
  value: 'abc123',
  expires: new Date(Date.now() + 3600 * 1000), // 1 hour from now
});

// Chrome 145+ — relative maxAge in seconds
await cookieStore.set({
  name: 'session',
  value: 'abc123',
  maxAge: 3600,  // 1 hour — relative, no clock dependency
});

// Works for short-lived cookies too
await cookieStore.set({ name: 'csrf', value: 'xyz', maxAge: 60 }); // 1 minute

// Session cookie (no expiry — deleted when browser closes)
await cookieStore.set({ name: 'temp', value: '123' }); // no maxAge, no expires

// Delete a cookie by setting maxAge: 0
await cookieStore.set({ name: 'old', value: '', maxAge: 0 });

references

• ChromeStatus entry
• MDN — CookieStore.set()
• Cookie Store API spec (WICG)