facebook/react · error · Error

514

514

Error message

Cannot access ${String(name)} on the server. You cannot dot into a temporary client reference from a server component. You can only pass the value through to the client.

What it means

On the server, temporary references are Proxy objects that let opaque client-held values (a File from a form, a client-created object) be passed back toward the client untouched. The proxy's get trap permits only a Context Provider identity check and 'then' (so async functions may return the value); reading any other property means the server is trying to use the value, which it cannot, so the trap throws naming the accessed property.

Source

Thrown at packages/react-server/src/ReactFlightServerTemporaryReferences.js:80

        // $FlowFixMe[prop-missing]
        return Object.prototype[Symbol.toPrimitive];
      case Symbol.toStringTag:
        // $FlowFixMe[prop-missing]
        return Object.prototype[Symbol.toStringTag];
      case 'Provider':
        // Context.Provider === Context in React, so return the same reference.
        // This allows server components to render <ClientContext.Provider>
        // which will be serialized and executed on the client.
        return receiver;
      case 'then':
        // Allow returning a temporary reference from an async function
        // Unlike regular Client References, a Promise would never have been serialized as
        // an opaque Temporary Reference, but instead would have been serialized as a
        // Promise on the server and so doesn't hit this path. So we can assume this wasn't
        // a Promise on the client.
        return undefined;
    }
    throw new Error(
      // eslint-disable-next-line react-internal/safe-string-coercion
      `Cannot access ${String(name)} on the server. ` +
        'You cannot dot into a temporary client reference from a server component. ' +
        'You can only pass the value through to the client.',
    );
  },
  set: function () {
    throw new Error(
      'Cannot assign to a temporary client reference from a server module.',
    );
  },
};

export function createTemporaryReference<T>(
  temporaryReferences: TemporaryReferenceSet,
  id: string,
): TemporaryReference<T> {
  const reference: TemporaryReference<any> = Object.defineProperties(

View on GitHub (pinned to eafeac097b)

Solutions

  1. Do not read or destructure the value on the server — pass it through to a Client Component prop.
  2. If file metadata is needed server-side, read the actual File entry from the original FormData instead of the temp ref.
  3. Exclude temporary references from logging/serialization; log only their identity or id key.

Example fix

// before — Server Component reads the value
function Files({fileRef}) { return <p>{fileRef.name}</p>; }

// after — the client reads it
function Files({fileRef}) { return <FileMeta fileRef={fileRef} />; }
// FileMeta.tsx
'use client';
export function FileMeta({fileRef}) { return <p>{fileRef.name}</p>; }
Defensive patterns

Strategy: try-catch

Validate before calling

// Track which decoded values are temporary references by identity BEFORE touching them.
const tempRefs = new WeakMap<object, string>();
const args = await decodeReply(formData, {temporaryReferences: tempRefs});
const opaque = new Set(args.filter(a => typeof a === 'object' && a !== null && tempRefs.has(a)));

Type guard

export function isTemporaryReference(v: unknown, store: WeakMap<object, string>): boolean {
  return typeof v === 'object' && v !== null && store.has(v); // WeakMap.has performs no property access on the proxy
}

Try / catch

try {
  return fileRef.name;
} catch (e) {
  if (String((e as Error)?.message).startsWith('Cannot access')) {
    return undefined; // treat as opaque, pass through untouched
  }
  throw e;
}

Prevention

When it happens

Trigger: Inside a Server Component or action: const {file} = args; file.name — any property read or destructuring on a temporary reference; for...in, spread, or logging with util.inspect/console.dir over a temp ref (inspectors read properties).

Common situations: Trying to inspect an uploaded file's name/size server-side after decoding an action reply; logging decoded action arguments wholesale; passing temp refs through feature-detecting utility code.

Related errors

AI-assisted analysis of facebook/react@eafeac097b (2026-08-21). Data as JSON: /api/errors/e38d19acd7073a45. Report an issue: GitHub.