facebook/react · error · Error

The React Server cannot be used outside a react-server envir

Error message

The React Server cannot be used outside a react-server environment. You must configure Node.js using the `--conditions react-server` flag.

What it means

The source-form guard for the './server' entry: the exports map maps 'react-server-dom-parcel/server' to the real writer only under the react-server condition; every other resolution lands on this file, which throws on import with instructions to run Node with --conditions react-server.

Source

Thrown at packages/react-server-dom-parcel/server.js:10

/**
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @flow
 */

throw new Error(
  'The React Server cannot be used outside a react-server environment. ' +
    'You must configure Node.js using the `--conditions react-server` flag.',
);

View on GitHub (pinned to eafeac097b)

Solutions

Run with node --conditions react-server (or NODE_OPTIONS)
Configure your test runner to resolve with the react-server condition for server-side tests
Or target the explicit .node/.edge/.browser subpath variants directly

Example fix

// before
"scripts": { "start": "node server.mjs" }

// after
"scripts": { "start": "node --conditions react-server server.mjs" }

Defensive patterns

Strategy: validation

Validate before calling

const flags = process.execArgv.concat((process.env.NODE_OPTIONS || '').split(' '));
if (!flags.some(a => a.includes('react-server'))) {
  throw new Error('Start with --conditions react-server before loading react-server-dom-parcel/server');
}

Try / catch

try {
  const server = await import('react-server-dom-parcel/server');
} catch (e) {
  if (/react-server environment/.test(e.message)) {
    throw new Error('Restart with --conditions react-server');
  }
  throw e;
}

Prevention

Keep the flag in every npm script that imports the server entry
Configure jest/vitest to resolve with the react-server condition for server tests
Fail fast at boot with the flag check instead of at first import

When it happens

Trigger: import ... from 'react-server-dom-parcel/server' evaluated without the react-server Node condition active — plain node, a bundler whose conditionNames omit it, or a runner (jest/vitest) that resolves conditions differently.

Common situations: Missing the flag in start scripts; test configs without customExportConditions/conditions; bundling server code with client condition sets.

Related errors

AI-assisted analysis of facebook/react@eafeac097b (2026-08-21). Data as JSON: /api/errors/0ef5efb718c95f58. Report an issue: GitHub.