Emitter.test.ts

test('Emitter', () => {
  const emitter = new Emitter()

  let counter = 0
  const increment = () => counter += 1

  // test the handler being fired
  emitter.on('increment', increment)
  emitter.emit('increment')
  expect(counter).toBe(1)

  // test that the handler isn't fired after being unassigned
  emitter.off('increment', increment)
  emitter.emit('increment')
  expect(counter).toBe(1)

  // test that once unbinds after being fired
  emitter.once('increment', increment)
  emitter.emit('increment')
  expect(counter).toBe(2)
  emitter.emit('increment')
  expect(counter).toBe(2)

  // test getListenerCount
  emitter.on('increment', increment)
  emitter.on('increment', increment)
  emitter.on('increment', increment)
  emitter.on('notincrement', increment)
  expect(emitter.getListenerCount('increment')).toBe(3)
  expect(emitter.getListenerCount('notincrement')).toBe(1)
})