jestjs/jest · error · TypeError

`jest.runOnlyPendingTimersAsync()` is not available when usi

Error message

`jest.runOnlyPendingTimersAsync()` is not available when using legacy fake timers.

What it means

TypeError thrown by `jest.runOnlyPendingTimersAsync()` when legacy fake timers are active. The async variant is a modern-fake-timers-only API.

Source

Thrown at packages/jest-runtime/src/internals/JestGlobals.ts:401

      runAllTimersAsync: async () => {
        const fakeTimers = _getFakeTimers();

        if (fakeTimers === this.environment.fakeTimersModern) {
          await fakeTimers.runAllTimersAsync();
        } else {
          throw new TypeError(
            '`jest.runAllTimersAsync()` is not available when using legacy fake timers.',
          );
        }
      },
      runOnlyPendingTimers: () => _getFakeTimers().runOnlyPendingTimers(),
      runOnlyPendingTimersAsync: async () => {
        const fakeTimers = _getFakeTimers();

        if (fakeTimers === this.environment.fakeTimersModern) {
          await fakeTimers.runOnlyPendingTimersAsync();
        } else {
          throw new TypeError(
            '`jest.runOnlyPendingTimersAsync()` is not available when using legacy fake timers.',
          );
        }
      },
      setMock: (moduleName, mock) => setMockFactory(moduleName, () => mock),
      setSystemTime: now => {
        const fakeTimers = _getFakeTimers();

        if (fakeTimers === this.environment.fakeTimersModern) {
          fakeTimers.setSystemTime(now);
        } else {
          throw new TypeError(
            '`jest.setSystemTime()` is not available when using legacy fake timers.',
          );
        }
      },
      setTimeout,
      setTimerTickMode: (

View on GitHub (pinned to f49721c78e)

Solutions

1. Switch to modern fake timers: `jest.useFakeTimers()` (default).
2. If you must keep legacy timers, use the sync `jest.runOnlyPendingTimers()` instead.

Example fix

// before
jest.useFakeTimers({ legacyFakeTimers: true });
await jest.runOnlyPendingTimersAsync(); // throws

// after
jest.useFakeTimers();
await jest.runOnlyPendingTimersAsync();

// Gate async timer APIs on modern timers
function modernOnly(fn) {
  // ensure config does not set legacyFakeTimers: true
  return fn();
}

When it happens

Trigger: Calling `jest.runOnlyPendingTimersAsync()` while `legacyFakeTimers: true` is in effect.

Common situations: Project-wide legacy timer config combined with tests using the async pending-timer flush.

Related errors

• `jest.advanceTimersByTimeAsync()` is not available when usin
• `jest.advanceTimersToNextTimerAsync()` is not available when
• `jest.runAllTimersAsync()` is not available when using legac
• `jest.advanceTimersToNextFrame()` is not available when usin
• `jest.getRealSystemTime()` is not available when using legac

AI-assisted analysis of jestjs/jest@f49721c78e (2026-08-03). Data as JSON: /data/errors/3a3a55c08284c251.json. Report an issue: GitHub.