js search in nav

search.js

let searchBox = document.querySelector(".searchBox");
let filterSearch, nav, linkCollection;
function processResults() {
  {#input = document.getElementById("mySearch");#}
  filterSearch = searchBox.value.toUpperCase();
  nav = document.querySelector(".leftnav");
  linkCollection = nav.getElementsByClassName("menuitem");
  Array.from(linkCollection).forEach(element => {
     if (element.innerHTML.toUpperCase().indexOf(filterSearch) > -1) {
        element.style.display = "";
     } else {
        element.style.display = "none";
     }
  });
}
searchBox.addEventListener("keyup", () => {
  processResults();
});