Recall the right memory for the right user

WHAT YOU WILL BUILD

A small memory lookup with identity, version, and expiration boundaries.

Memory is stored information retrieved under a policy. This example chooses the latest unexpired value for one user and key. It makes updates and expiration visible without implying that a model remembers data outside the supplied context.

FOLLOW ALONG

Work through the example.

1. 01

   Inspect the three records

   Alex has an older English preference and a newer French preference. Blair has a Spanish preference with an even higher version. The user filter must happen before selecting the latest value.

2. 02

   Recall at time twelve

   Run the example. Alex receives French. The higher version belonging to Blair cannot override Alex's preference.

3. 03

   Recall after expiration

   At time twenty-one, both Alex records have expired and the lookup returns null. The application should ask again or use a stated default; it must not borrow another user's record.

4. 04

   Test a correction

   Add Alex's version-three preference with a later expiry. Update your expected answer and verify the correction wins. Add a deletion test before adapting this to persistent storage.

THE COMPLETE LAB

Run it locally.

Run this command from the folder containing your downloaded file:

node agent-memory.mjs

// SaveMyToken local lab. Run with Node.js 22 or newer.
import assert from "node:assert/strict";

const records = [
  { user: "alex", key: "language", value: "English", version: 1, expires: 10 },
  { user: "alex", key: "language", value: "French", version: 2, expires: 20 },
  { user: "blair", key: "language", value: "Spanish", version: 3, expires: 30 },
];
function recall(user, key, now) {
  return records.filter(row => row.user === user && row.key === key && row.expires > now)
    .sort((a, b) => b.version - a.version)[0]?.value ?? null;
}
assert.equal(recall("alex", "language", 12), "French");
assert.equal(recall("alex", "language", 21), null);
assert.equal(recall("unknown", "language", 12), null);
console.log("Alex at t=12:", recall("alex", "language", 12));
console.log("Alex at t=21:", recall("alex", "language", 21));

Expected output for the unchanged example

Alex at t=12: French
Alex at t=21: null

The assertions also check the baseline behavior. After changing an input, predict the result and update the relevant assertion.

EXPLAIN WHAT YOU LEARNED

Interview practice

Try answering aloud before opening the reference answer. These are original learning questions, not a record of any employer's interviews.