Class FakeClock

A clock that moves only when a test calls FakeClock.advance.

now starts at start (Unix milliseconds, default 2026-01-01T00:00:00Z) and monotonic at zero; sleep waits until advance passes its deadline, and advance wakes sleepers in deadline order, letting each woken task run before the time moves on.

Example

const clock = new FakeClock();
const done = clock.sleep(5_000);
await clock.advance(5_000);
await done;
clock.monotonic(); // 5000

Implements

Clock

Index

Constructors

constructor

new FakeClock(start?: number): FakeClock
Creates the clock.
Parameters
- start: number = ...
  The wall time at monotonic zero, Unix milliseconds.
Returns FakeClock

Accessors

sleepers

get sleepers(): number
The number of tasks currently waiting in sleep.

Returns number

Methods

advance

advance(ms: number): Promise<void>
Moves the time forward by ms, waking sleepers in deadline order.
Parameters
- ms: number
  How far to move; must not be negative.
Returns Promise<void>
Throws
RangeError when ms is negative.

monotonic

monotonic(): number
Returns the milliseconds advanced since the start.

Returns number
Implementation of Clock.monotonic

now

now(): number
Returns the fake wall time, Unix milliseconds.

Returns number
Implementation of Clock.now

sleep

sleep(ms: number, signal?: AbortSignal): Promise<void>
Waits until the clock has advanced by ms.
Parameters
- ms: number
  The wait; zero or negative yields once.
- Optionalsignal: AbortSignal
  Optional abort signal; an abort rejects with its reason.
Returns Promise<void>
Implementation of Clock.sleep

Class FakeClock

Example

Implements

Index

Constructors

Accessors

Methods

Constructors

constructor

Parameters

Returns FakeClock

Accessors

sleepers

Returns number

Methods

advance

Parameters

Returns Promise<void>

Throws

monotonic

Returns number

now

Returns number

sleep

Parameters

Returns Promise<void>

Settings

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