facebook/react · warning

You did not run Node.js with the `--conditions react-server`

Error message

You did not run Node.js with the `--conditions react-server` flag. Any "react-server" override will only work with ESM imports.

What it means

Identical check in the react-server-dom-unbundled loader (ReactFlightUnbundledNodeLoader.js:82): when the resolve hook does not see 'react-server' among context.conditions, it appends it per-call for ESM resolution and warns once that without the node --conditions react-server flag the override only works for ESM imports, because require() never goes through the hooks.

Source

Thrown at packages/react-server-dom-unbundled/src/ReactFlightUnbundledNodeLoader.js:82

let stashedResolve: null | ResolveFunction = null;

export async function resolve(
  specifier: string,
  context: ResolveContext,
  defaultResolve: ResolveFunction,
): Promise<{url: string}> {
  // We stash this in case we end up needing to resolve export * statements later.
  stashedResolve = defaultResolve;

  if (!context.conditions.includes('react-server')) {
    context = {
      ...context,
      conditions: [...context.conditions, 'react-server'],
    };
    if (!warnedAboutConditionsFlag) {
      warnedAboutConditionsFlag = true;
      // eslint-disable-next-line react-internal/no-production-logging
      console.warn(
        'You did not run Node.js with the `--conditions react-server` flag. ' +
          'Any "react-server" override will only work with ESM imports.',
      );
    }
  }
  return await defaultResolve(specifier, context, defaultResolve);
}

export async function getSource(
  url: string,
  context: GetSourceContext,
  defaultGetSource: GetSourceFunction,
): Promise<{source: Source}> {
  // We stash this in case we end up needing to resolve export * statements later.
  stashedGetSource = defaultGetSource;
  return defaultGetSource(url, context, defaultGetSource);
}

View on GitHub (pinned to eafeac097b)

Solutions

1. Run node with --conditions react-server for every process that registers this loader
2. Centralize the flag in package.json scripts and CI commands
3. Set NODE_OPTIONS='--conditions react-server' for environments you cannot pass CLI flags to
4. Ensure the server entry is ESM so the injected condition actually applies

Example fix

// before
node --import ./loader.mjs server.cjs

// after
node --conditions react-server --import ./loader.mjs server.mjs

const hasServerCondition = process.execArgv
  .join(' ')
  .includes('react-server');
if (!hasServerCondition) {
  throw new Error('Missing --conditions react-server on the node process');
}

When it happens

Trigger: Using register() from react-server-dom-unbundled/server (unbundled RSC protocol) in a node process started without --conditions react-server; first import resolution after registration emits the warning.

Common situations: RSC servers built on the unbundled wire protocol; dev servers restarted by watchers that drop node flags; deployments where the npm start script differs from the local dev command.

Related errors

• You did not run Node.js with the `--conditions react-server`
• You did not run Node.js with the `--conditions react-server`
• Expected resolve to have been called before transformSource
• Expected the transformed source to be a string.
• Attempted to call the default export of ${url} from the serv

AI-assisted analysis of facebook/react@eafeac097b (2026-08-21). Data as JSON: /api/errors/d41b5bfeaa714046. Report an issue: GitHub.