How to create a search bar that DOESN'T GIVE RESULTS WHEN NOTHING IS WRITTEN ON IT.

Question

My JavaScript code so far:

function search() {

// Declare variables
var input, filter, ul, li, a, i;
input = document.getElementById('input');
filter = input.value.toUpperCase();
ul = document.getElementById('ops');
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 = "block";
}

else{

li[i].style.display = "none";
}

if (a.innerHTML.toUpperCase().indexOf(filter) <= -1) {
li[i].style.display = "none";
}
}

}

Answer 1

<input type=search>
<button>Search</button>

don't gives you any result

Answer 2

Confused about the question format, but
//eventListener for keydown
if (event.key = "Enter" || event.keyCode == 13) {
if (input.value != "") {
search();
}
}