jestjs/jest · error · TypeError

`jest.runAllTimersAsync()` is not available when using legac

Error message

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

What it means

TypeError thrown by `jest.runAllTimersAsync()` when legacy fake timers are active. The async variant of `runAllTimers` is implemented only on the modern fake timers backend.

Source

Thrown at packages/jest-runtime/src/internals/JestGlobals.ts:389

        const fakeTimers = _getFakeTimers();

        if (fakeTimers === this.environment.fakeTimers) {
          fakeTimers.runAllImmediates();
        } else {
          throw new TypeError(
            '`jest.runAllImmediates()` is only available when using legacy fake timers.',
          );
        }
      },
      runAllTicks: () => _getFakeTimers().runAllTicks(),
      runAllTimers: () => _getFakeTimers().runAllTimers(),
      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 => {

View on GitHub (pinned to f49721c78e)

Solutions

1. Switch to modern fake timers: `jest.useFakeTimers()` (default).
2. If legacy timers are required, use the sync `jest.runAllTimers()` instead of the async variant.

Example fix

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

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

// Ensure modern timers before async timer APIs
function useModernTimersThen(fn) {
  return async () => {
    jest.useFakeTimers(); // modern
    await fn();
  };
}

When it happens

Trigger: Calling `jest.runAllTimersAsync()` after `jest.useFakeTimers({ legacyFakeTimers: true })` or with `fakeTimers.legacyFakeTimers: true` in config.

Common situations: Defaulting to legacy timers project-wide while newer tests use the async timer API for async test ergonomics.

Related errors

• `jest.advanceTimersByTimeAsync()` is not available when usin
• `jest.advanceTimersToNextTimerAsync()` is not available when
• `jest.runOnlyPendingTimersAsync()` is not available when usi
• `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/36b7376686dec3e4.json. Report an issue: GitHub.