facebook/react · error · Error

Symbols cannot be passed to a Server Function without a temp

Error message

Symbols cannot be passed to a Server Function without a temporary reference set. Pass a TemporaryReferenceSet to the options.

What it means

Symbols have no wire representation in the Flight reply format, so a symbol argument can only be sent by registering it in a TemporaryReferenceSet that the server shares. If temporaryReferences is undefined (or the symbol is not reachable via a dedupe-able parent path), serializeReply throws, naming the missing option. The same constraint applies to symbol values anywhere in the argument tree, not just at the top level.

Source

Thrown at packages/react-client/src/ReactFlightReplyClient.js:866

        'Client Functions cannot be passed directly to Server Functions. ' +
          'Only Functions passed from the Server can be passed back again.',
      );
    }

    if (typeof value === 'symbol') {
      if (temporaryReferences !== undefined && key.indexOf(':') === -1) {
        // TODO: If the property name contains a colon, we don't dedupe. Escape instead.
        const parentReference = writtenObjects.get(parent);
        if (parentReference !== undefined) {
          // If the parent has a reference, we can refer to this object indirectly
          // through the property name inside that parent.
          const reference = parentReference + ':' + key;
          // Store this object so that the server can refer to it later in responses.
          writeTemporaryReference(temporaryReferences, reference, value);
          return serializeTemporaryReferenceMarker();
        }
      }
      throw new Error(
        'Symbols cannot be passed to a Server Function without a ' +
          'temporary reference set. Pass a TemporaryReferenceSet to the options.' +
          (__DEV__ ? describeObjectForErrorMessage(parent, key) : ''),
      );
    }

    if (typeof value === 'bigint') {
      return serializeBigInt(value);
    }

    throw new Error(
      `Type ${typeof value} is not supported as an argument to a Server Function.`,
    );
  }

  function serializeModel(model: ReactServerValue, id: number): string {
    if (typeof model === 'object' && model !== null) {
      const reference = serializeByValueID(id);

View on GitHub (pinned to eafeac097b)

Solutions

1. Pass a TemporaryReferenceSet in the encodeReply/callServer options so symbols can be registered and referenced by id
2. Send a string instead: symbol.description or a stable registry key, and rebuild the symbol on the server from a shared table
3. Audit argument trees for symbols before sending (typeof v === 'symbol') and map them explicitly
4. If the symbol is only used as a property key locally, restructure to plain string keys for data that crosses the boundary

Example fix

// before
const THEMES = {dark: Symbol('dark'), light: Symbol('light')};
await setTheme(THEMES.dark); // throws

// after
await setTheme('dark'); // string token; server maps it back to its own symbol

// Reject or map symbols before the call crosses the boundary
function assertNoBareSymbols(v: unknown, seen = new Set()): void {
  if (typeof v === 'symbol') {
    throw new Error('Symbol argument requires a TemporaryReferenceSet - or send a string token');
  }
  if (v === null || typeof v !== 'object' || seen.has(v)) return;
  seen.add(v);
  Object.values(v).forEach(c => assertNoBareSymbols(c, seen));
}

const isSymbol = (v: unknown): v is symbol => typeof v === 'symbol';

When it happens

Trigger: Passing a symbol as a Server Function argument or inside one: await setTheme(SYMBOLS.dark); library objects that internally use symbol keys/values (registries, well-known symbols) leaking into the payload without a temporaryReferences set.

Common situations: Sending theme/feature tokens implemented as symbols; styling libraries that key slots with symbols; enum-like symbols shared between client and server code; forgetting the options object entirely when hand-rolling encodeReply.

Related errors

• Missing a temporary reference set but the RSC response retur
• React Element cannot be passed to Server Functions from the
• Only plain objects, and a few built-ins, can be passed to Se
• Client Functions cannot be passed directly to Server Functio
• Type ${typeof value} is not supported as an argument to a Se

AI-assisted analysis of facebook/react@eafeac097b (2026-08-21). Data as JSON: /api/errors/067acde6258d9ff9. Report an issue: GitHub.