---
outline: deep
---

# Vi

Vitest provides utility functions to help you out through its `vi` helper. You can access it globally (when [globals configuration](/config/#globals) is enabled), or import it from `vitest` directly:

```js
import { vi } from 'vitest'
```

## Mock Modules

This section describes the API that you can use when [mocking a module](/guide/mocking#modules). Beware that Vitest doesn't support mocking modules imported using `require()`.

### vi.mock

- **Type**: `(path: string, factory?: (importOriginal: () => unknown) => unknown) => void`

Substitutes all imported modules from provided `path` with another module. You can use configured Vite aliases inside a path. The call to `vi.mock` is hoisted, so it doesn't matter where you call it. It will always be executed before all imports. If you need to reference some variables outside of its scope, you can define them inside [`vi.hoisted`](#vi-hoisted) and reference them inside `vi.mock`.

::: warning
`vi.mock` works only for modules that were imported with the `import` keyword. It doesn't work with `require`.

In order to hoist `vi.mock`, Vitest statically analyzes your files. It indicates that `vi` that was not directly imported from the `vitest` package (for example, from some utility file) cannot be used. Use `vi.mock` with `vi` imported from `vitest`, or enable [`globals`](/config/#globals) config option.

Vitest will not mock modules that were imported inside a [setup file](/config/#setupfiles) because they are cached by the time a test file is running. You can call [`vi.resetModules()`](#vi-resetmodules) inside [`vi.hoisted`](#vi-hoisted) to clear all module caches before running a test file.
:::

::: warning
The [browser mode](/guide/browser) does not presently support mocking modules. You can track this feature in the GitHub [issue](https://github.com/vitest-dev/vitest/issues/3046).
:::

If `factory` is defined, all imports will return its result. Vitest calls factory only once and caches results for all subsequent imports until [`vi.unmock`](#vi-unmock) or [`vi.doUnmock`](#vi-dounmock) is called.

Unlike in `jest`, the factory can be asynchronous. You can use [`vi.importActual`](#vi-importactual) or a helper with the factory passed in as the first argument, and get the original module inside.

```js twoslash
import { vi } from 'vitest'
// ---cut---
// when using JavaScript

vi.mock('./path/to/module.js', async (importOriginal) => {
  const mod = await importOriginal()
  return {
    ...mod,
    // replace some exports
    namedExport: vi.fn(),
  }
})
```

```ts
// when using TypeScript

vi.mock('./path/to/module.js', async (importOriginal) => {
  const mod = await importOriginal<typeof import('./path/to/module.js')>()
  return {
    ...mod,
    // replace some exports
    namedExport: vi.fn(),
  }
})
```

::: warning
`vi.mock` is hoisted (in other words, _moved_) to **top of the file**. It means that whenever you write it (be it inside `beforeEach` or `test`), it will actually be called before that.

This also means that you cannot use any variables inside the factory that are defined outside the factory.

If you need to use variables inside the factory, try [`vi.doMock`](#vi-domock). It works the same way but isn't hoisted. Beware that it only mocks subsequent imports.

You can also reference variables defined by `vi.hoisted` method if it was declared before `vi.mock`:

```ts
import { namedExport } from './path/to/module.js'

const mocks = vi.hoisted(() => {
  return {
    namedExport: vi.fn(),
  }
})

vi.mock('./path/to/module.js', () => {
  return {
    namedExport: mocks.namedExport,
  }
})

vi.mocked(namedExport).mockReturnValue(100)

expect(namedExport()).toBe(100)
expect(namedExport).toBe(mocks.namedExport)
```
:::

::: warning
If you are mocking a module with default export, you will need to provide a `default` key within the returned factory function object. This is an ES module-specific caveat; therefore, `jest` documentation may differ as `jest` uses CommonJS modules. For example,

```ts
vi.mock('./path/to/module.js', () => {
  return {
    default: { myDefaultKey: vi.fn() },
    namedExport: vi.fn(),
    // etc...
  }
})
```
:::

If there is a `__mocks__` folder alongside a file that you are mocking, and the factory is not provided, Vitest will try to find a file with the same name in the `__mocks__` subfolder and use it as an actual module. If you are mocking a dependency, Vitest will try to find a `__mocks__` folder in the [root](/config/#root) of the project (default is `process.cwd()`). You can tell Vitest where the dependencies are located through the [deps.moduleDirectories](/config/#deps-moduledirectories) config option.

For example, you have this file structure:

```
- __mocks__
  - axios.js
- src
  __mocks__
    - increment.js
  - increment.js
- tests
  - increment.test.js
```

If you call `vi.mock` in a test file without a factory provided, it will find a file in the `__mocks__` folder to use as a module:

```ts
// increment.test.js
import { vi } from 'vitest'

// axios is a default export from `__mocks__/axios.js`
import axios from 'axios'

// increment is a named export from `src/__mocks__/increment.js`
import { increment } from '../increment.js'

vi.mock('axios')
vi.mock('../increment.js')

axios.get(`/apples/${increment(1)}`)
```

::: warning
Beware that if you don't call `vi.mock`, modules **are not** mocked automatically. To replicate Jest's automocking behaviour, you can call `vi.mock` for each required module inside [`setupFiles`](/config/#setupfiles).
:::

If there is no `__mocks__` folder or a factory provided, Vitest will import the original module and auto-mock all its exports. For the rules applied, see [algorithm](/guide/mocking#automocking-algorithm).

### vi.doMock

- **Type**: `(path: string, factory?: (importOriginal: () => unknown) => unknown) => void`

The same as [`vi.mock`](#vi-mock), but it's not hoisted to the top of the file, so you can reference variables in the global file scope. The next [dynamic import](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/import) of the module will be mocked.

::: warning
This will not mock modules that were imported before this was called. Don't forget that all static imports in ESM are always [hoisted](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import#hoisting), so putting this before static import will not force it to be called before the import:

```ts
vi.doMock('./increment.js') // this will be called _after_ the import statement

import { increment } from './increment.js'
```
:::

```ts
// ./increment.js
export function increment(number) {
  return number + 1
}
```

```ts
import { beforeEach, test } from 'vitest'
import { increment } from './increment.js'

// the module is not mocked, because vi.doMock is not called yet
increment(1) === 2

let mockedIncrement = 100

beforeEach(() => {
  // you can access variables inside a factory
  vi.doMock('./increment.js', () => ({ increment: () => ++mockedIncrement }))
})

test('importing the next module imports mocked one', async () => {
  // original import WAS NOT MOCKED, because vi.doMock is evaluated AFTER imports
  expect(increment(1)).toBe(2)
  const { increment: mockedIncrement } = await import('./increment.js')
  // new dynamic import returns mocked module
  expect(mockedIncrement(1)).toBe(101)
  expect(mockedIncrement(1)).toBe(102)
  expect(mockedIncrement(1)).toBe(103)
})
```

### vi.mocked

- **Type**: `<T>(obj: T, deep?: boolean) => MaybeMockedDeep<T>`
- **Type**: `<T>(obj: T, options?: { partial?: boolean; deep?: boolean }) => MaybePartiallyMockedDeep<T>`

Type helper for TypeScript. Just returns the object that was passed.

When `partial` is `true` it will expect a `Partial<T>` as a return value. By default, this will only make TypeScript believe that the first level values are mocked. You can pass down `{ deep: true }` as a second argument to tell TypeScript that the whole object is mocked, if it actually is.

```ts
import example from './example.js'

vi.mock('./example.js')

test('1 + 1 equals 10', async () => {
  vi.mocked(example.calc).mockReturnValue(10)
  expect(example.calc(1, '+', 1)).toBe(10)
})
```

### vi.importActual

- **Type**: `<T>(path: string) => Promise<T>`

Imports module, bypassing all checks if it should be mocked. Can be useful if you want to mock module partially.

```ts
vi.mock('./example.js', async () => {
  const axios = await vi.importActual('./example.js')

  return { ...axios, get: vi.fn() }
})
```

### vi.importMock

- **Type**: `<T>(path: string) => Promise<MaybeMockedDeep<T>>`

Imports a module with all of its properties (including nested properties) mocked. Follows the same rules that [`vi.mock`](#vi-mock) does. For the rules applied, see [algorithm](/guide/mocking#automocking-algorithm).

### vi.unmock

- **Type**: `(path: string) => void`

Removes module from the mocked registry. All calls to import will return the original module even if it was mocked before. This call is hoisted to the top of the file, so it will only unmock modules that were defined in `setupFiles`, for example.

### vi.doUnmock

- **Type**: `(path: string) => void`

The same as [`vi.unmock`](#vi-unmock), but is not hoisted to the top of the file. The next import of the module will import the original module instead of the mock. This will not unmock previously imported modules.

```ts
// ./increment.js
export function increment(number) {
  return number + 1
}
```

```ts
import { increment } from './increment.js'

// increment is already mocked, because vi.mock is hoisted
increment(1) === 100

// this is hoisted, and factory is called before the import on line 1
vi.mock('./increment.js', () => ({ increment: () => 100 }))

// all calls are mocked, and `increment` always returns 100
increment(1) === 100
increment(30) === 100

// this is not hoisted, so other import will return unmocked module
vi.doUnmock('./increment.js')

// this STILL returns 100, because `vi.doUnmock` doesn't reevaluate a module
increment(1) === 100
increment(30) === 100

// the next import is unmocked, now `increment` is the original function that returns count + 1
const { increment: unmockedIncrement } = await import('./increment.js')

unmockedIncrement(1) === 2
unmockedIncrement(30) === 31
```

### vi.resetModules

- **Type**: `() => Vitest`

Resets modules registry by clearing the cache of all modules. This allows modules to be reevaluated when reimported. Top-level imports cannot be re-evaluated. Might be useful to isolate modules where local state conflicts between tests.

```ts
import { vi } from 'vitest'

import { data } from './data.js' // Will not get reevaluated beforeEach test

beforeEach(() => {
  vi.resetModules()
})

test('change state', async () => {
  const mod = await import('./some/path.js') // Will get reevaluated
  mod.changeLocalState('new value')
  expect(mod.getLocalState()).toBe('new value')
})

test('module has old state', async () => {
  const mod = await import('./some/path.js') // Will get reevaluated
  expect(mod.getLocalState()).toBe('old value')
})
```

::: warning
Does not reset mocks registry. To clear mocks registry, use [`vi.unmock`](#vi-unmock) or [`vi.doUnmock`](#vi-dounmock).
:::

### vi.dynamicImportSettled

Wait for all imports to load. Useful, if you have a synchronous call that starts importing a module that you cannot wait otherwise.

```ts
import { expect, test } from 'vitest'

// cannot track import because Promise is not returned
function renderComponent() {
  import('./component.js').then(({ render }) => {
    render()
  })
}

test('operations are resolved', async () => {
  renderComponent()
  await vi.dynamicImportSettled()
  expect(document.querySelector('.component')).not.toBeNull()
})
```

::: tip
If during a dynamic import another dynamic import is initiated, this method will wait until all of them are resolved.

This method will also wait for the next `setTimeout` tick after the import is resolved so all synchronous operations should be completed by the time it's resolved.
:::

## Mocking Functions and Objects

This section describes how to work with [method mocks](/api/mock) and replace environmental and global variables.

### vi.fn

- **Type:** `(fn?: Function) => Mock`

Creates a spy on a function, though can be initiated without one. Every time a function is invoked, it stores its call arguments, returns, and instances. Also, you can manipulate its behavior with [methods](/api/mock).
If no function is given, mock will return `undefined`, when invoked.

```ts twoslash
import { expect, vi } from 'vitest'
// ---cut---
const getApples = vi.fn(() => 0)

getApples()

expect(getApples).toHaveBeenCalled()
expect(getApples).toHaveReturnedWith(0)

getApples.mockReturnValueOnce(5)

const res = getApples()
expect(res).toBe(5)
expect(getApples).toHaveNthReturnedWith(2, 5)
```

### vi.isMockFunction

- **Type:** `(fn: Function) => boolean`

Checks that a given parameter is a mock function. If you are using TypeScript, it will also narrow down its type.

### vi.clearAllMocks

Will call [`.mockClear()`](/api/mock#mockclear) on all spies. This will clear mock history, but not reset its implementation to the default one.

### vi.resetAllMocks

Will call [`.mockReset()`](/api/mock#mockreset) on all spies. This will clear mock history and reset its implementation to an empty function (will return `undefined`).

### vi.restoreAllMocks

Will call [`.mockRestore()`](/api/mock#mockrestore) on all spies. This will clear mock history and reset its implementation to the original one.

### vi.spyOn

- **Type:** `<T, K extends keyof T>(object: T, method: K, accessType?: 'get' | 'set') => MockInstance`

Creates a spy on a method or getter/setter of an object similar to [`vi.fn()`](#vi-fn). It returns a [mock function](/api/mock).

```ts twoslash
import { expect, vi } from 'vitest'
// ---cut---
let apples = 0
const cart = {
  getApples: () => 42,
}

const spy = vi.spyOn(cart, 'getApples').mockImplementation(() => apples)
apples = 1

expect(cart.getApples()).toBe(1)

expect(spy).toHaveBeenCalled()
expect(spy).toHaveReturnedWith(1)
```

::: tip
You can call [`vi.restoreAllMocks`](#vi-restoreallmocks) inside [`afterEach`](/api/#aftereach) (or enable [`test.restoreMocks`](/config/#restoreMocks)) to restore all methods to their original implementations. This will restore the original [object descriptor](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty), so you won't be able to change method's implementation:

```ts
const cart = {
  getApples: () => 42,
}

const spy = vi.spyOn(cart, 'getApples').mockReturnValue(10)

console.log(cart.getApples()) // 10
vi.restoreAllMocks()
console.log(cart.getApples()) // 42
spy.mockReturnValue(10)
console.log(cart.getApples()) // still 42!
```
:::

### vi.stubEnv <Badge type="info">0.26.0+</Badge> {#vi-stubenv}

- **Type:** `(name: string, value: string) => Vitest`

Changes the value of environmental variable on `process.env` and `import.meta.env`. You can restore its value by calling `vi.unstubAllEnvs`.

```ts
import { vi } from 'vitest'

// `process.env.NODE_ENV` and `import.meta.env.NODE_ENV`
// are "development" before calling "vi.stubEnv"

vi.stubEnv('NODE_ENV', 'production')

process.env.NODE_ENV === 'production'
import.meta.env.NODE_ENV === 'production'
// doesn't change other envs
import.meta.env.MODE === 'development'
```

:::tip
You can also change the value by simply assigning it, but you won't be able to use `vi.unstubAllEnvs` to restore previous value:

```ts
import.meta.env.MODE = 'test'
```
:::

### vi.unstubAllEnvs <Badge type="info">0.26.0+</Badge> {#vi-unstuballenvs}

- **Type:** `() => Vitest`

Restores all `import.meta.env` and `process.env` values that were changed with `vi.stubEnv`. When it's called for the first time, Vitest remembers the original value and will store it, until `unstubAllEnvs` is called again.

```ts
import { vi } from 'vitest'

// `process.env.NODE_ENV` and `import.meta.env.NODE_ENV`
// are "development" before calling stubEnv

vi.stubEnv('NODE_ENV', 'production')

process.env.NODE_ENV === 'production'
import.meta.env.NODE_ENV === 'production'

vi.stubEnv('NODE_ENV', 'staging')

process.env.NODE_ENV === 'staging'
import.meta.env.NODE_ENV === 'staging'

vi.unstubAllEnvs()

// restores to the value that were stored before the first "stubEnv" call
process.env.NODE_ENV === 'development'
import.meta.env.NODE_ENV === 'development'
```

### vi.stubGlobal

- **Type:** `(name: string | number | symbol, value: unknown) => Vitest`

Changes the value of global variable. You can restore its original value by calling `vi.unstubAllGlobals`.

```ts twoslash
import { vi } from 'vitest'

// `innerWidth` is "0" before calling stubGlobal

vi.stubGlobal('innerWidth', 100)

innerWidth === 100
globalThis.innerWidth === 100
// if you are using jsdom or happy-dom
window.innerWidth === 100
```

:::tip
You can also change the value by simply assigning it to `globalThis` or `window` (if you are using `jsdom` or `happy-dom` environment), but you won't be able to use `vi.unstubAllGlobals` to restore original value:

```ts
globalThis.innerWidth = 100
// if you are using jsdom or happy-dom
window.innerWidth = 100
```
:::

### vi.unstubAllGlobals <Badge type="info">0.26.0+</Badge> {#vi-unstuballglobals}

- **Type:** `() => Vitest`

Restores all global values on `globalThis`/`global` (and `window`/`top`/`self`/`parent`, if you are using `jsdom` or `happy-dom` environment) that were changed with `vi.stubGlobal`. When it's called for the first time, Vitest remembers the original value and will store it, until `unstubAllGlobals` is called again.

```ts
import { vi } from 'vitest'

const Mock = vi.fn()

// IntersectionObserver is "undefined" before calling "stubGlobal"

vi.stubGlobal('IntersectionObserver', Mock)

IntersectionObserver === Mock
global.IntersectionObserver === Mock
globalThis.IntersectionObserver === Mock
// if you are using jsdom or happy-dom
window.IntersectionObserver === Mock

vi.unstubAllGlobals()

globalThis.IntersectionObserver === undefined
'IntersectionObserver' in globalThis === false
// throws ReferenceError, because it's not defined
IntersectionObserver === undefined
```

## Fake Timers

This sections descibes how to work with [fake timers](/guide/mocking#timers).

### vi.advanceTimersByTime

- **Type:** `(ms: number) => Vitest`

This method will invoke every initiated timer until the specified number of milliseconds is passed or the queue is empty - whatever comes first.

```ts twoslash
import { vi } from 'vitest'
// ---cut---
let i = 0
setInterval(() => console.log(++i), 50)

vi.advanceTimersByTime(150)

// log: 1
// log: 2
// log: 3
```

### vi.advanceTimersByTimeAsync

- **Type:** `(ms: number) => Promise<Vitest>`

This method will invoke every initiated timer until the specified number of milliseconds is passed or the queue is empty - whatever comes first. This will include asynchronously set timers.

```ts twoslash
import { vi } from 'vitest'
// ---cut---
let i = 0
setInterval(() => Promise.resolve().then(() => console.log(++i)), 50)

await vi.advanceTimersByTimeAsync(150)

// log: 1
// log: 2
// log: 3
```

### vi.advanceTimersToNextTimer

- **Type:** `() => Vitest`

Will call next available timer. Useful to make assertions between each timer call. You can chain call it to manage timers by yourself.

```ts twoslash
import { vi } from 'vitest'
// ---cut---
let i = 0
setInterval(() => console.log(++i), 50)

vi.advanceTimersToNextTimer() // log: 1
  .advanceTimersToNextTimer() // log: 2
  .advanceTimersToNextTimer() // log: 3
```

### vi.advanceTimersToNextTimerAsync

- **Type:** `() => Promise<Vitest>`

Will call next available timer and wait until it's resolved if it was set asynchronously. Useful to make assertions between each timer call.

```ts twoslash
import { expect, vi } from 'vitest'
// ---cut---
let i = 0
setInterval(() => Promise.resolve().then(() => console.log(++i)), 50)

await vi.advanceTimersToNextTimerAsync() // log: 1
expect(console.log).toHaveBeenCalledWith(1)

await vi.advanceTimersToNextTimerAsync() // log: 2
await vi.advanceTimersToNextTimerAsync() // log: 3
```

### vi.getTimerCount

- **Type:** `() => number`

Get the number of waiting timers.

### vi.clearAllTimers

Removes all timers that are scheduled to run. These timers will never run in the future.

### vi.getMockedSystemTime

- **Type**: `() => Date | null`

Returns mocked current date that was set using `setSystemTime`. If date is not mocked the method will return `null`.

### vi.getRealSystemTime

- **Type**: `() => number`

When using `vi.useFakeTimers`, `Date.now` calls are mocked. If you need to get real time in milliseconds, you can call this function.

### vi.runAllTicks

- **Type:** `() => Vitest`

Calls every microtask that was queued by `process.nextTick`. This will also run all microtasks scheduled by themselves.

### vi.runAllTimers

- **Type:** `() => Vitest`

This method will invoke every initiated timer until the timer queue is empty. It means that every timer called during `runAllTimers` will be fired. If you have an infinite interval, it will throw after 10 000 tries (can be configured with [`fakeTimers.loopLimit`](/config/#faketimers-looplimit)).

```ts twoslash
import { vi } from 'vitest'
// ---cut---
let i = 0
setTimeout(() => console.log(++i))
const interval = setInterval(() => {
  console.log(++i)
  if (i === 3)
    clearInterval(interval)
}, 50)

vi.runAllTimers()

// log: 1
// log: 2
// log: 3
```

### vi.runAllTimersAsync

- **Type:** `() => Promise<Vitest>`

This method will asynchronously invoke every initiated timer until the timer queue is empty. It means that every timer called during `runAllTimersAsync` will be fired even asynchronous timers. If you have an infinite interval,
it will throw after 10 000 tries (can be configured with [`fakeTimers.loopLimit`](/config/#faketimers-looplimit)).

```ts twoslash
import { vi } from 'vitest'
// ---cut---
setTimeout(async () => {
  console.log(await Promise.resolve('result'))
}, 100)

await vi.runAllTimersAsync()

// log: result
```

### vi.runOnlyPendingTimers

- **Type:** `() => Vitest`

This method will call every timer that was initiated after [`vi.useFakeTimers`](#vi-usefaketimers) call. It will not fire any timer that was initiated during its call.

```ts twoslash
import { vi } from 'vitest'
// ---cut---
let i = 0
setInterval(() => console.log(++i), 50)

vi.runOnlyPendingTimers()

// log: 1
```

### vi.runOnlyPendingTimersAsync

- **Type:** `() => Promise<Vitest>`

This method will asynchronously call every timer that was initiated after [`vi.useFakeTimers`](#vi-usefaketimers) call, even asynchronous ones. It will not fire any timer that was initiated during its call.

```ts twoslash
import { vi } from 'vitest'
// ---cut---
setTimeout(() => {
  console.log(1)
}, 100)
setTimeout(() => {
  Promise.resolve().then(() => {
    console.log(2)
    setInterval(() => {
      console.log(3)
    }, 40)
  })
}, 10)

await vi.runOnlyPendingTimersAsync()

// log: 2
// log: 3
// log: 3
// log: 1
```

### vi.setSystemTime

- **Type**: `(date: string | number | Date) => void`

If fake timers are enabled, this method simulates a user changing the system clock (will affect date related API like `hrtime`, `performance.now` or `new Date()`) - however, it will not fire any timers. If fake timers are not enabled, this method will only mock `Date.*` calls.

Useful if you need to test anything that depends on the current date - for example [Luxon](https://github.com/moment/luxon/) calls inside your code.

```ts twoslash
import { expect, vi } from 'vitest'
// ---cut---
const date = new Date(1998, 11, 19)

vi.useFakeTimers()
vi.setSystemTime(date)

expect(Date.now()).toBe(date.valueOf())

vi.useRealTimers()
```

### vi.useFakeTimers

- **Type:** `(config?: FakeTimerInstallOpts) => Vitest`

To enable mocking timers, you need to call this method. It will wrap all further calls to timers (such as `setTimeout`, `setInterval`, `clearTimeout`, `clearInterval`, `setImmediate`, `clearImmediate`, and `Date`) until [`vi.useRealTimers()`](#vi-userealtimers) is called.

Mocking `nextTick` is not supported when running Vitest inside `node:child_process` by using `--pool=forks`. NodeJS uses `process.nextTick` internally in `node:child_process` and hangs when it is mocked. Mocking `nextTick` is supported when running Vitest with `--pool=threads`.

The implementation is based internally on [`@sinonjs/fake-timers`](https://github.com/sinonjs/fake-timers).

::: tip
Since version `0.35.0` `vi.useFakeTimers()` no longer automatically mocks `process.nextTick`.
It can still be mocked by specifying the option in `toFake` argument: `vi.useFakeTimers({ toFake: ['nextTick'] })`.
:::

### vi.isFakeTimers <Badge type="info">0.34.5+</Badge> {#vi-isfaketimers}

- **Type:** `() => boolean`

Returns `true` if fake timers are enabled.

### vi.useRealTimers

- **Type:** `() => Vitest`

When timers are run out, you may call this method to return mocked timers to its original implementations. All timers that were scheduled before will be discarded.

## Miscellaneous

A set of useful helper functions that Vitest provides.

### vi.waitFor <Badge type="info">0.34.5+</Badge> {#vi-waitfor}

- **Type:** `<T>(callback: WaitForCallback<T>, options?: number | WaitForOptions) => Promise<T>`

Wait for the callback to execute successfully. If the callback throws an error or returns a rejected promise it will continue to wait until it succeeds or times out.

This is very useful when you need to wait for some asynchronous action to complete, for example, when you start a server and need to wait for it to start.

```ts
import { expect, test, vi } from 'vitest'
import { createServer } from './server.js'

test('Server started successfully', async () => {
  const server = createServer()

  await vi.waitFor(
    () => {
      if (!server.isReady)
        throw new Error('Server not started')

      console.log('Server started')
    },
    {
      timeout: 500, // default is 1000
      interval: 20, // default is 50
    }
  )
  expect(server.isReady).toBe(true)
})
```

It also works for asynchronous callbacks

```ts
// @vitest-environment jsdom

import { expect, test, vi } from 'vitest'
import { getDOMElementAsync, populateDOMAsync } from './dom.js'

test('Element exists in a DOM', async () => {
  // start populating DOM
  populateDOMAsync()

  const element = await vi.waitFor(async () => {
    // try to get the element until it exists
    const element = await getDOMElementAsync() as HTMLElement | null
    expect(element).toBeTruthy()
    expect(element.dataset.initialized).toBeTruthy()
    return element
  }, {
    timeout: 500, // default is 1000
    interval: 20, // default is 50
  })
  expect(element).toBeInstanceOf(HTMLElement)
})
```

If `vi.useFakeTimers` is used, `vi.waitFor` automatically calls `vi.advanceTimersByTime(interval)` in every check callback.

### vi.waitUntil <Badge type="info">0.34.5+</Badge> {#vi-waituntil}

- **Type:** `<T>(callback: WaitUntilCallback<T>, options?: number | WaitUntilOptions) => Promise<T>`

This is similar to `vi.waitFor`, but if the callback throws any errors, execution is immediately interrupted and an error message is received. If the callback returns falsy value, the next check will continue until truthy value is returned. This is useful when you need to wait for something to exist before taking the next step.

Look at the example below. We can use `vi.waitUntil` to wait for the element to appear on the page, and then we can do something with the element.

```ts twoslash
import { expect, test, vi } from 'vitest'

test('Element render correctly', async () => {
  const element = await vi.waitUntil(
    () => document.querySelector('.element'),
    {
      timeout: 500, // default is 1000
      interval: 20, // default is 50
    }
  )

  // do something with the element
  expect(element.querySelector('.element-child')).toBeTruthy()
})
```

### vi.hoisted <Badge type="info">0.31.0+</Badge> {#vi-hoisted}

- **Type**: `<T>(factory: () => T) => T`

All static `import` statements in ES modules are hoisted to the top of the file, so any code that is defined before the imports will actually be executed after imports are evaluated.

However, it can be useful to invoke some side effects like mocking dates before importing a module.

To bypass this limitation, you can rewrite static imports into dynamic ones like this:

```diff
callFunctionWithSideEffect()
- import { value } from './some/module.js'
+ const { value } = await import('./some/module.js')
```

When running `vitest`, you can do this automatically by using `vi.hoisted` method.

```diff
- callFunctionWithSideEffect()
import { value } from './some/module.js'
+ vi.hoisted(() => callFunctionWithSideEffect())
```

This method returns the value that was returned from the factory. You can use that value in your `vi.mock` factories if you need easy access to locally defined variables:

```ts
import { expect, vi } from 'vitest'
import { originalMethod } from './path/to/module.js'

const { mockedMethod } = vi.hoisted(() => {
  return { mockedMethod: vi.fn() }
})

vi.mock('./path/to/module.js', () => {
  return { originalMethod: mockedMethod }
})

mockedMethod.mockReturnValue(100)
expect(originalMethod()).toBe(100)
```

Note that this method can also be called asynchronously even if your environment doesn't support top-level await:

```ts
const promised = await vi.hoisted(async () => {
  const response = await fetch('https://jsonplaceholder.typicode.com/posts')
  return response.json()
})
```

### vi.setConfig

- **Type**: `RuntimeConfig`

Updates config for the current test file. This method supports only config options that will affect the current test file:

```ts
vi.setConfig({
  allowOnly: true,
  testTimeout: 10_000,
  hookTimeout: 10_000,
  clearMocks: true,
  restoreMocks: true,
  fakeTimers: {
    now: new Date(2021, 11, 19),
    // supports the whole object
  },
  maxConcurrency: 10,
  sequence: {
    hooks: 'stack'
    // supports only "sequence.hooks"
  }
})
```

### vi.resetConfig

- **Type**: `RuntimeConfig`

If [`vi.setConfig`](#vi-setconfig) was called before, this will reset config to the original state.
