What causes "Fallback response for "${table}" is not an object" in BloopAI/vibe-kanban?

Make the fallback endpoint return { " ": [ ...rows ] } keyed by the shape's table name.

Fallback response for "${table}" is not an object

Error message

Fallback response for "${table}" is not an object

What it means

extractFallbackRows validates the JSON payload returned by a table's fallback endpoint: it must be an object, because the row array is looked up under the payload[table] key. This error is thrown when the fallback HTTP endpoint succeeded (2xx) but its body is not a JSON object (e.g. null, an array, a string, or invalid shape parsed as a primitive).

Source

Thrown at packages/web-core/src/shared/lib/electric/collections.ts:412

  for (const row of rows) {
    syncParams.write({
      type: 'insert',
      value: row,
      metadata: {},
    });
  }

  syncParams.commit();
  syncParams.markReady();
}

function extractFallbackRows(
  payload: unknown,
  table: string
): Array<ElectricRow> {
  if (!payload || typeof payload !== 'object') {
    throw new Error(`Fallback response for "${table}" is not an object`);
  }

  const rows = (payload as Record<string, unknown>)[table];
  if (!Array.isArray(rows)) {
    throw new Error(`Fallback response missing "${table}" array`);
  }

  return rows as Array<ElectricRow>;
}

async function parseResponseError(
  response: Response,
  fallbackMessage: string
): Promise<string> {
  try {
    const body = (await response.json()) as {
      message?: string;
      error?: string;

View on GitHub (pinned to 4deb7eca8f)

Solutions

Make the fallback endpoint return { "<table>": [ ...rows ] } keyed by the shape's table name.
Verify the `table` value in the ShapeDefinition matches the key the server uses in the response.
Log the actual payload on failure to see what the endpoint returned.
Check for proxies/middleware rewriting successful responses (auth walls returning HTML with 200).

Example fix

// before (server)
res.json(rows);
// after (server)
res.json({ tasks: rows }); // key must equal the shape's table name

Defensive patterns

Strategy: type-guard

Validate before calling

const res = await fetch(fallbackUrl);
const payload = await res.json();
if (!payload || typeof payload !== 'object' || Array.isArray(payload)) {
  throw new Error('Fallback endpoint must return an object keyed by table name');
}

Type guard

function isFallbackPayload(payload: unknown, table: string): payload is Record<string, ElectricRow[]> {
  return (
    typeof payload === 'object' && payload !== null && !Array.isArray(payload) &&
    Array.isArray((payload as Record<string, unknown>)[table])
  );
}

Try / catch

try {
  const payload = await response.json();
  if (!isFallbackPayload(payload, table)) {
    console.error('Unexpected fallback payload', payload);
    return;
  }
} catch (e) {
  reportSyncError(e);
}

Prevention

Contract-test every fallback endpoint's response shape
Keep the response key identical to the shape's table name
Never return bare arrays, null, or HTML with 200 from fallback routes
Log raw payloads when adding new fallback sources

When it happens

Trigger: Fallback endpoint returns a bare JSON array instead of { [table]: [...] }; endpoint returns null; endpoint returns plain text/HTML with 200; response.json() parses to a primitive; a proxy intercepts and returns a non-standard body.

Common situations: Backend route returning `res.json(rows)` instead of keyed object; API gateway/error page served with 200; mismatch between the shape's `table` name and the key the server actually uses (e.g. table 'tasks' but server returns { items: [...] }); server upgrade changed response envelope.

Related errors

AI-assisted analysis of BloopAI/vibe-kanban@4deb7eca8f (2026-08-29). Data as JSON: /api/errors/a2dc478b3e7de544. Report an issue: GitHub.