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index.test.js
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const { JSDOM } = require("jsdom");
const dom = new JSDOM(`<!DOCTYPE html><p>Hello world</p>`);
const originalWindow = { ...window }
const windowSpy = jest.spyOn(global, 'window', 'get')
const { addScrollListener, removeScrollListener } = require('./index');
const waitRAF = () => new Promise(resolve => requestAnimationFrame(resolve))
describe('When addScrollListener adds a callback (y-scroll)', () => {
const mockCallback = jest.fn()
beforeAll(() => {
addScrollListener(mockCallback)
})
it('it should fire on vertical scroll', async () => {
windowSpy.mockImplementation(() => ({
...originalWindow,
pageYOffset: -40
}))
await waitRAF();
expect(mockCallback).toHaveBeenCalled()
})
it('it shouldn\'t fire twice for a single vertical scroll', async () => {
await waitRAF();
expect(mockCallback).toHaveBeenCalledTimes(1)
})
it('it should fire on subsequent vertical scrolls', async () => {
windowSpy.mockImplementation(() => ({
...originalWindow,
pageYOffset: 0
}))
await waitRAF();
expect(mockCallback).toHaveBeenCalledTimes(2)
})
afterAll(() => {
removeScrollListener(mockCallback)
jest.clearAllMocks();
})
})
describe('When addScrollListener adds a callback (x-scroll)', () => {
const mockCallback = jest.fn()
beforeAll(() => {
addScrollListener(mockCallback)
})
it('it should fire on horizontal scroll', async () => {
windowSpy.mockImplementation(() => ({
...originalWindow,
pageXOffset: -40
}))
await waitRAF();
expect(mockCallback).toHaveBeenCalled()
})
it('it shouldn\'t fire twice for a single horizontal scroll', async () => {
await waitRAF();
expect(mockCallback).toHaveBeenCalledTimes(1)
})
it('it should fire on subsequent horizontal scrolls', async () => {
windowSpy.mockImplementation(() => ({
...originalWindow,
pageXOffset: 0
}))
await waitRAF();
expect(mockCallback).toHaveBeenCalledTimes(2)
})
afterAll(() => {
removeScrollListener(mockCallback)
jest.clearAllMocks();
})
})
describe('When removeScrollListener removes a callback', () => {
const mockCallback = jest.fn()
beforeAll(() => {
addScrollListener(mockCallback)
removeScrollListener(mockCallback)
})
it('it shouldn\'t fire on scroll', async () => {
windowSpy.mockImplementation(() => ({
...originalWindow,
pageYOffset: -40
}))
await waitRAF();
expect(mockCallback).toHaveBeenCalledTimes(0)
})
afterAll(() => {
jest.clearAllMocks();
})
})
describe('When a callback throws an error with breakOnError', () => {
const mockCallback = jest.fn().mockImplementation(() => {
throw new Error('Test Error')
})
beforeAll(() => {
addScrollListener(mockCallback, true)
})
it('it should not error on scroll', async () => {
windowSpy.mockImplementation(() => ({
...originalWindow,
pageYOffset: 1234
}))
await waitRAF();
expect(mockCallback).toHaveBeenCalledTimes(1)
})
it('it should not be called a second time on scroll', async () => {
windowSpy.mockImplementation(() => ({
...originalWindow,
pageYOffset: 500
}))
await waitRAF();
expect(mockCallback).toHaveBeenCalledTimes(1)
})
afterAll(() => {
removeScrollListener(mockCallback)
jest.clearAllMocks();
})
})