gistfile1.txt

button.addEventListener('click', () => {
  Promise.resolve().then(() => console.log('P1'))
  console.log('L1')
})

button.addEventListener('click', () => {
  Promise.resolve().then(() => console.log('P2'))
  console.log('L2')
})

click button
L1 P1 L2 P2

button.click()
L1 L2 P1 P2