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async task is before rendering

    const btn = document.getElementById('btn')
    const box = document.getElementById('box')
    btn.addEventListener('click', callback, false)
    function callback() {
      box.style.display = 'none'
      box.style.display = 'block'
      box.style.display = 'none'
      box.style.display = 'block'
      box.style.display = 'none'
      box.style.display = 'block'
    }

    const btn2 = document.getElementById('btn2')
    btn2.addEventListener('click', callback2, false)
    function callback2() {
      box.style.transform = 'translateX(800px)'
      box.style.transition = 'transform 1s ease-in-out'
      box.style.transform = 'translateX(100px)'
    }