Adding Keypress for up/down arrow to select results and also allow to press enter to select

Thanks in advance for any help or suggestions as I am still new to javascripts. I am trying to modify the below script to also allow up/down keypress and enter key to select result.

<script>
$(document).ready(function(){
    $('.search-box input[type="text"]').on("keyup input", function(){
        /* Get input value on change */
        var inputVal = $(this).val();
        var resultDropdown = $(this).siblings(".result");
        if(inputVal.length){
            $.get("backend-search.php", {term: inputVal}).done(function(data){
                // Display the returned data in browser
                resultDropdown.html(data);
            });
        } else{
            resultDropdown.empty();
        }
    });

    // Set search input value on click of result item
    $(document).on("click", ".result p", function(){
        $(this).parents(".search-box").find('input[type="text"]').val($(this).text());
        $(this).parent(".result").empty();
    });
});
</script>

I found the below script online, and have been trying to incorporate it or modify it to work with the above script, but have had no luck.

 inp.addEventListener("input", function(e) {
      var a, b, i, val = this.value;
      /*close any already open lists of autocompleted values*/
      closeAllLists();
      if (!val) { return false;}
      currentFocus = -1;
      /*create a DIV element that will contain the items (values):*/
      a = document.createElement("DIV");
      a.setAttribute("id", this.id + "autocomplete-list");
      a.setAttribute("class", "autocomplete-items");
      /*append the DIV element as a child of the autocomplete container:*/
      this.parentNode.appendChild(a);
      /*for each item in the array...*/
      for (i = 0; i < arr.length; i++) {
        /*check if the item starts with the same letters as the text field value:*/
        if (arr[i].substr(0, val.length).toUpperCase() == val.toUpperCase()) {
          /*create a DIV element for each matching element:*/
          b = document.createElement("DIV");
          /*make the matching letters bold:*/
          b.innerHTML = "<strong>" + arr[i].substr(0, val.length) + "</strong>";
          b.innerHTML += arr[i].substr(val.length);
          /*insert a input field that will hold the current array item's value:*/
          b.innerHTML += "<input type='hidden' value='" + arr[i] + "'>";
          /*execute a function when someone clicks on the item value (DIV element):*/
              b.addEventListener("click", function(e) {
              /*insert the value for the autocomplete text field:*/
              inp.value = this.getElementsByTagName("input")[0].value;
              /*close the list of autocompleted values,
              (or any other open lists of autocompleted values:*/
              closeAllLists();
          });
          a.appendChild(b);
        }
      }
  });
  /*execute a function presses a key on the keyboard:*/
  inp.addEventListener("keydown", function(e) {
      var x = document.getElementById(this.id + "autocomplete-list");
      if (x) x = x.getElementsByTagName("div");
      if (e.keyCode == 40) {
        /*If the arrow DOWN key is pressed,
        increase the currentFocus variable:*/
        currentFocus++;
        /*and and make the current item more visible:*/
        addActive(x);
      } else if (e.keyCode == 38) { //up
        /*If the arrow UP key is pressed,
        decrease the currentFocus variable:*/
        currentFocus--;
        /*and and make the current item more visible:*/
        addActive(x);
      } else if (e.keyCode == 13) {
        /*If the ENTER key is pressed, prevent the form from being submitted,*/
        e.preventDefault();
        if (currentFocus > -1) {
          /*and simulate a click on the "active" item:*/
          if (x) x[currentFocus].click();
        }
      }

I have tried this:

    $(document).ready(function(){
    $('.search-box input[type="text"]').on("keyup input", function(){
        /* Get input value on change */
        var inputVal = $(this).val();
        var resultDropdown = $(this).siblings(".result");
        if(inputVal.length){
            $.get("backend-search.php", {term: inputVal}).done(function(data){
                // Display the returned data in browser
                resultDropdown.html(data);
            });
        } else{
            resultDropdown.empty();
        }
    });
    // Set search input value on click of result item
    $(document).on("click", ".result p", function(){
        $(this).parents(".search-box").find('input[type="text"]').val($(this).text());
        $(this).parent(".result").empty();
    });
});
  /*execute a function presses a key on the keyboard:*/
  inp.addEventListener("keydown", function(e) {
      var x = document.getElementById(this.id + "result");
      if (x) x = x.getElementsByTagName("div");
      if (e.keyCode == 40) {
        /*If the arrow DOWN key is pressed,
        increase the currentFocus variable:*/
        currentFocus++;
        /*and and make the current item more visible:*/
        addActive(x);
      } else if (e.keyCode == 38) { //up
        /*If the arrow UP key is pressed,
        decrease the currentFocus variable:*/
        currentFocus--;
        /*and and make the current item more visible:*/
        addActive(x);
      } else if (e.keyCode == 13) {
        /*If the ENTER key is pressed, prevent the form from being submitted,*/
        e.preventDefault();
        if (currentFocus > -1) {
          /*and simulate a click on the "active" item:*/
          if (x) x[currentFocus].click();
        }
      }
  });