@react-spring/mock-raf

A simple mock for requestAnimationFrame testing with fake timers.

Adapted with gratitude from react-motion.

Example

To use with jest/jasmine and react-spring:

import createMockRaf from '@react-spring/mock-raf'
import { Globals, FrameLoop, SpringValue } from 'react-spring'

let mockRaf
beforeEach(() => {
  mockRaf = createMockRaf()
  Globals.assign({
    now: mockRaf.now,
    performanceNow: mockRaf.now,
    requestAnimationFrame: mockRaf.raf,
    cancelAnimationFrame: mockRaf.cancel,
    frameLoop: new FrameLoop(),
  })
})

it('animates from 0 to 1', () => {
  const value = new SpringValue(0)
  value.start(1)

  expect(value.get()).toBe(0)
  mockRaf.flush()
  expect(value.get()).toBe(1)
})

API

createMockRaf()

Creates a mockRaf instance, exposing the functions you'll use to interact with the mock.

Returns:

• now()
• raf()
• cancel()
• step()

const mockRaf = createMockRaf()

now()

Returns the current now value of the mock. Starts at 0 and increases with each step() taken. Useful for stubbing out performance.now() or a polyfill when using requestAnimationFrame with timers.

raf()

Replacement for requestAnimationFrame or a polyfill. Adds a callback to be fired on the next step.

cancel()

Replacement for cancelAnimationFrame or a polyfill. Removes all currently scheduled requestAnimationFrame callbacks from the queue.

flush()

Continuously iterate the requestAnimationFrame queue until empty.

Useful for jumping to the end of an animation (or group of animations).

step(options)

Takes requestAnimationFrame steps. Fires currently queued callbacks for each step and increments now time for each step. The primary way to interact with a mockRaf instance for testing.

Options

step() takes an optional options object:

time

Type: Number Default: 1000 / 60

The time that should pass during each requestAnimationFrame step in milliseconds. Default is roughly equivalent to default browser behavior.

count

Type: Number Default: 1

The number of steps to take.