project.js

<script>
function myFunction() {
  // Declare variables
  var input, filter, ul, li, a, i;
  input = document.getElementById("mySearch");
  filter = input.value.toUpperCase();
  ul = document.getElementById("myMenu");
  li = ul.getElementsByTagName("li");

  // Loop through all list items, and hide those who don't match the search query
  for (i = 0; i < li.length; i++) {
    a = li[i].getElementsByTagName("a")[0];
    if (a.innerHTML.toUpperCase().indexOf(filter) > -1) {
      li[i].style.display = "";
    } else {
      li[i].style.display = "none";
    }
  }
}
</script>

//Get the button
let mybutton = document.getElementById("btn-back-to-top");

// When the user scrolls down 20px from the top of the document, show the button
window.onscroll = function () {
  scrollFunction();
};

function scrollFunction() {
  if (
    document.body.scrollTop > 20 ||
    document.documentElement.scrollTop > 20
  ) {
    mybutton.style.display = "block";
  } else {
    mybutton.style.display = "none";
  }
}
// When the user clicks on the button, scroll to the top of the document
mybutton.addEventListener("click", backToTop);

function backToTop() {
  document.body.scrollTop = 0;
  document.documentElement.scrollTop = 0;
}