function throttle(func, wait = 300) {
  let previous = 0
  return function() {
    let now = date.now()
    if (now - previous > wait) {
      func.apply(this, arguments)
      previous = now
    }
  }
}

window.onload = () => {
  const header = document.queryselector('.header')
  const { offsetheight } = header
  window.addeventlistener('scroll', throttle(function () {
    const initialtopvalue = 50
    const scrolly = window.scrolly
    console.log('scrolly', scrolly)
    if (scrolly > offsetheight + initialtopvalue) {
      header.classlist.add('sticky')
    } else {
      header.classlist.remove('sticky')
    }
  }))
}