What causes "Chess.com stats payload for ${kind}.last is not an object" in jackwener/OpenCLI?

Re-fetch fresh stats from the pub API; the documented shape has last as an object with rating/date

jackwener/OpenCLI · error · CommandExecutionError

Chess.com stats payload for ${kind}.last is not an object

Error message

Chess.com stats payload for ${kind}.last is not an object

What it means

Within summarizeStats(), the k.last field (most recent rating snapshot) may be absent, but if present it must be a plain object containing e.g. rating/date. This throw fires when k.last exists but is a non-object value (string, number, array). It is a strict shape check so downstream k.last?.rating access behaves predictably.

Source

Thrown at clis/chess/utils.js:76

        payload = await resp.json();
    } catch (error) {
        throw new CommandExecutionError(`Chess.com API returned malformed JSON for ${url}: ${error?.message || error}`);
    }
    if (!isPlainObject(payload)) {
        throw new CommandExecutionError(`Chess.com API returned an unexpected payload shape for ${url}`);
    }
    return payload;
}

/** Pull rating + record fields out of a stats sub-object (`chess_rapid` etc). */
export function summarizeStats(stats, kind) {
    const k = stats?.[kind];
    if (!k) return null;
    if (!isPlainObject(k)) {
        throw new CommandExecutionError(`Chess.com stats payload for ${kind} is not an object`);
    }
    if (!isOptionalPlainObject(k.last)) {
        throw new CommandExecutionError(`Chess.com stats payload for ${kind}.last is not an object`);
    }
    if (!isOptionalPlainObject(k.best)) {
        throw new CommandExecutionError(`Chess.com stats payload for ${kind}.best is not an object`);
    }
    if (!isOptionalPlainObject(k.record)) {
        throw new CommandExecutionError(`Chess.com stats payload for ${kind}.record is not an object`);
    }
    const record = isPlainObject(k.record) ? k.record : {};
    return {
        kind: kind.replace(/^chess_/, ''),
        rating_current: k.last?.rating ?? '',
        rating_best: k.best?.rating ?? '',
        wins: record.win ?? '',
        losses: record.loss ?? '',
        draws: record.draw ?? '',
    };
}

View on GitHub (pinned to 49907e53dc)

Solutions

Re-fetch fresh stats from the pub API; the documented shape has last as an object with rating/date
Inspect the offending value (typeof k.last) and fix the producer that flattened it
If building fixtures/mocks, use last: { rating: 1500, date: 1700000000 }
Patch the mapping layer if Chess.com altered the last field's structure

Example fix

// before
stats.chess_rapid.last = 1500; // flattened
// after
stats.chess_rapid.last = { rating: 1500, date: Math.floor(Date.now() / 1000) };

Defensive patterns

Strategy: validation

Validate before calling

const last = stats?.[kind]?.last;
if (last != null && (typeof last !== 'object' || Array.isArray(last))) {
  throw new Error(`${kind}.last must be an object like { rating, date }`);
}

Type guard

function hasValidLast(k) {
  return k?.last == null ||
    (typeof k.last === 'object' && !Array.isArray(k.last) && typeof k.last.rating === 'number');
}

Try / catch

try {
  const row = summarizeStats(stats, 'chess_rapid');
} catch (err) {
  if (String(err.message).includes('.last is not an object')) {
    console.warn('last section malformed; refetching stats');
    stats = await (await fetch(`${API_BASE}/player/${user}/stats`)).json();
  } else { throw err; }
}

Prevention

Keep last as { rating, date } objects; never flatten to a scalar rating
Re-fetch from the pub API instead of trusting old normalized caches
Validate shape when writing to cache, not only when reading
Check typeof before reassigning nested fields in pipelines

When it happens

Trigger: Payload from /pub/player/{username}/stats where stats[kind].last is a non-object truthy value, e.g. last: "1500" or last: [..], passed via rows() or row().

Common situations: Transformed/normalized cache where last was flattened to a scalar rating; schema change on Chess.com; test fixture built with wrong nesting; a spreadsheet/CSV round-trip turned the nested object into a scalar.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

AI-assisted analysis of jackwener/OpenCLI@49907e53dc (2026-08-29). Data as JSON: /api/errors/b2b97960b2a42421. Report an issue: GitHub.