FakeTimers

Summary

Handle returned by mock.timers.enable() for driving fake timers during a test. While enabled, setTimeout, setInterval, clearTimeout, clearInterval, and Date.now use the fake clock instead of the real one; timers fire only when the test calls advance (or advanceAsync).

Signature

interface FakeTimers {
  advance(ms: number): void;
  advanceAsync(ms: number): Promise<void>;
  restore(): void;
}

Methods

advance(ms: number): void

Advance the fake clock by ms milliseconds, synchronously firing every timer whose deadline is reached during the advance.

Parameters

ms

Number of milliseconds to advance.

advanceAsync(ms: number): Promise<void>

Like advance, but yields to microtasks between each timer firing so Promise continuations (and any timers they schedule) can settle before the next firing is processed. Use this when a callback awaits work that itself depends on the fake clock.

Parameters

ms

Number of milliseconds to advance.

restore(): void

Restore the original timer functions and the real clock. Called automatically after the test finishes; may also be called early to disable fake timers mid-test.