How to bake a cache layer using only rumors

This recipe creates one cache layer. It is not edible, but neither are most cache layers.

Ingredients

1. One stale response.
2. Two tablespoons of max-age.
3. A pinch of panic.
4. A monitoring dashboard nobody opens during normal business hours.

Method

const pantry = new Map();

export function remember(key, value, ttlMs) {
  pantry.set(key, {
    value,
    expiresAt: Date.now() + ttlMs,
  });
}

export function recall(key) {
  const entry = pantry.get(key);
  if (!entry || entry.expiresAt < Date.now()) {
    pantry.delete(key);
    return undefined;
  }

  return entry.value;
}

Warning

Do not season a cache with mystery invalidation unless you are ready to answer questions from your future self.

If the feature still feels slow, rename it to “eventually fresh” and write a blog post about tradeoffs.