need to use arrow keys to move through search suggestions

var searchIndex = ["404 Error", "Address Bar", "Ajax", "Apache", "Autoresponder", "BitTorrent", "Blog", "Bookmark", "Bot", "Broadband", "Captcha", "Certificate", "Client", "Cloud", "Cloud Computing", "CMS", "Cookie", "CSS", "Cyberspace", "Denial of Service", "DHCP", "Dial-up", "DNS Record", "Domain Name", "Download", "E-mail", "Facebook", "FiOS", "Firewall", "FTP", "Gateway", "Google", "Google Drive", "Gopher", "Hashtag", "Hit", "Home Page", "HTML", "HTTP", "HTTPS", "Hyperlink", "Hypertext", "ICANN", "Inbox", "Internet", "InterNIC", "IP", "IP Address", "IPv4", "IPv6", "IRC", "iSCSI", "ISDN", "ISP", "JavaScript", "jQuery", "Meta Search Engine", "Meta Tag", "Minisite", "Mirror", "Name Server", "Packet", "Page View", "Payload", "Phishing", "POP3", "Protocol", "Scraping", "Search Engine", "Social Networking", "Socket", "Spam", "Spider", "Spoofing", "SSH", "SSL", "Static Website", "Twitter", "XHTML"];

var input = document.getElementById("searchBox"),
  ul = document.getElementById("searchResults"),
  inputTerms, termsArray, prefix, terms, results, sortedResults;


var search = function() {
  inputTerms = input.value.toLowerCase();
  results = [];
  termsArray = inputTerms.split(' ');
  prefix = termsArray.length === 1 ? '' : termsArray.slice(0, -1).join(' ') + ' ';
  terms = termsArray[termsArray.length - 1].toLowerCase();

  for (var i = 0; i < searchIndex.length; i++) {
    var a = searchIndex[i].toLowerCase(),
      t = a.indexOf(terms);

    if (t > -1) {
      results.push(a);
    }
  }

  evaluateResults();
};

var evaluateResults = function() {
  if (results.length > 0 && inputTerms.length > 0 && terms.length !== 0) {
    sortedResults = results.sort(sortResults);
    appendResults();
  } else if (inputTerms.length > 0 && terms.length !== 0) {
    ul.innerHTML = '<li>Whoah! <strong>' +
      inputTerms +
      '</strong> is not in the index. <br><small><a href="http://google.com/search?q=' +
      encodeURIComponent(inputTerms) + '">Try Google?</a></small></li>';

  } else if (inputTerms.length !== 0 && terms.length === 0) {
    return;
  } else {
    clearResults();
  }
};

var sortResults = function(a, b) {
  if (a.indexOf(terms) < b.indexOf(terms)) return -1;
  if (a.indexOf(terms) > b.indexOf(terms)) return 1;
  return 0;
}

var appendResults = function() {
  clearResults();

  for (var i = 0; i < sortedResults.length && i < 5; i++) {
    var li = document.createElement("li"),
      result = prefix +
      sortedResults[i].toLowerCase().replace(terms, '<strong>'+ terms + '</strong>');

    li.innerHTML = result;

    ul.appendChild(li);
  }
  $('li').click(function(e) {
    $('input').val($(this).text());
  });
  if (ul.className !== "term-list") {
    ul.className = "term-list";
  }
};

var clearResults = function() {
  ul.className = "term-list hidden";
  ul.innerHTML = '';
};

input.addEventListener("keyup", search, false);





var li = $('li');
var liSelected;
$(window).keydown(function(e) {
  if (e.which === 40) {
    if (liSelected) {
      liSelected.removeClass('selected');
      next = liSelected.next();
      if (next.length > 0) {
        liSelected = next.addClass('selected');
      } else {
        liSelected = li.eq(0).addClass('selected');
      }
    } else {
      liSelected = li.eq(0).addClass('selected');
    }
  } else if (e.which === 38) {
    if (liSelected) {
      liSelected.removeClass('selected');
      next = liSelected.prev();
      if (next.length > 0) {
        liSelected = next.addClass('selected');
      } else {
        liSelected = li.last().addClass('selected');
      }
    } else {
      liSelected = li.last().addClass('selected');
    }
  }
});

.search-field,
.term-list {
  -moz-border-radius: 3px;
  -webkit-border-radius: 3px;
  border-radius: 3px;
}

body {
  text-align: center;
  background: #f2f2f2;
}

.title {
  width: 100%;
  margin: 3em 0 1em;
  text-align: center;
  font-family: "Arvo", "Helvetica Neue", Helvetica, arial, sans-serif;
  font-size: 170%;
  font-weight: 400;
  color: #2a5ba3;
  text-shadow: #fff 1px 1px 0px, #ddd 2px 2px, #ddd 3px 3px 1px;
}

.search-field {
  display: block;
  width: 30%;
  margin: 1em auto 0;
  padding: 0.5em 10px;
  border: 1px solid #999;
  font-size: 130%;
  font-family: "Arvo", "Helvetica Neue", Helvetica, arial, sans-serif;
  font-weight: 400;
  color: #3e8ce0;
}

.term-list {
  list-style: none inside;
  width: 30%;
  margin: 0 auto 2em;
  padding: 5px 10px 0;
  text-align: left;
  color: #777;
  background: #fff;
  border: 1px solid #ddd;
  font-family: "Arvo", "Helvetica Neue", Helvetica, arial, sans-serif;
  font-weight: 400;
}

.term-list li {
  padding: 0.5em 0;
  border-bottom: 1px solid #eee;
}

li.selected {
  background: yellow
}

.term-list strong {
  color: #444;
  font-weight: 700;
}

.hidden {
  display: none;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<h1 class="title">AutoComplete Me</h1>
<input type="text" id="searchBox" class="search-field" autoFocus />
<ul id="searchResults" class="term-list hidden"></ul>