jestjs/jest · error · Error

Custom export conditions specified but they are not an array

Error message

Custom export conditions specified but they are not an array of strings

What it means

The Node environment performs the same customExportConditions validation as the JSDOM base (default `['node','node-addons']`). It throws at index.ts:211 when the value is present but not an Array<string>, preventing a malformed resolver config from silently resolving the wrong package entry.

Source

Thrown at packages/jest-environment-node/src/index.ts:211

      // @ts-expect-error - it's readonly - but we have checked above that it's not there
      globalSymbol.asyncDispose = globalSymbol.for('nodejs.asyncDispose');
      // @ts-expect-error - it's readonly - but we have checked above that it's not there
      globalSymbol.dispose = globalSymbol.for('nodejs.dispose');
    }

    // Node's error-message stack size is limited at 10, but it's pretty useful
    // to see more than that when a test fails.
    global.Error.stackTraceLimit = 100;

    if ('customExportConditions' in projectConfig.testEnvironmentOptions) {
      const {customExportConditions} = projectConfig.testEnvironmentOptions;
      if (
        Array.isArray(customExportConditions) &&
        customExportConditions.every(isString)
      ) {
        this._configuredExportConditions = customExportConditions;
      } else {
        throw new Error(
          'Custom export conditions specified but they are not an array of strings',
        );
      }
    }

    this.moduleMocker = new ModuleMocker(global);

    this.fakeTimers = new LegacyFakeTimers({
      config: projectConfig,
      global,
      moduleMocker: this.moduleMocker,
      timerConfig: {
        idToRef: timerIdToRef,
        refToId: timerRefToId,
      },
    });

    this.fakeTimersModern = new ModernFakeTimers({

View on GitHub (pinned to f49721c78e)

Solutions

1. Use an array of strings, e.g. `customExportConditions: ['node', 'node-addons']`.
2. Drop the option to keep the environment defaults.
3. Validate the config shape with a startup check that `Array.isArray` and `every(isString)`.

Example fix

// before
testEnvironmentOptions: { customExportConditions: 'node' }

// after
testEnvironmentOptions: { customExportConditions: ['node'] }

const opts = config.testEnvironmentOptions?.customExportConditions;
if (opts != null && (!Array.isArray(opts) || opts.every === undefined || !opts.every((x: unknown) => typeof x === 'string'))) {
  throw new TypeError('customExportConditions must be string[]');
}

const isStringArray = (v: unknown): v is string[] => Array.isArray(v) && v.every(x => typeof x === 'string');

When it happens

Trigger: Setting `testEnvironmentOptions.customExportConditions` to a non-array or to an array containing non-strings while using `jest-environment-node`.

Common situations: Sharing a config across environments where one path used a string; tooling that injects a single condition string; misreading the docs and passing `'node-addons'` instead of `['node-addons']`.

Related errors

• Custom export conditions specified but they are not an array
• jest.config.mts requires native TypeScript support. Ensure y
• JSDOM did not return a Window object
• Resolver located at ${resolver} does not export anything
• Resolver located at ${resolver} does not export a function o

AI-assisted analysis of jestjs/jest@f49721c78e (2026-08-03). Data as JSON: /data/errors/8835300b461a195c.json. Report an issue: GitHub.