#4.html

  <script>
  function SearchEnabled() {
	 if(document.getElementById("ext_search_txt").value==="") {
            document.getElementById('ext_search').disabled = true;
        } else {
            document.getElementById('ext_search').disabled = false;
        }
  }
  </script>

<form name="form" action="" method="post">
          <div class="input-group mb-3 box-shadow">
            <input type="text" id="ext_search_txt" name="ext_search" onkeyup="SearchEnabled()" class="form-control" placeholder="<?php print(ExternalSearchPlaceholder);?>" aria-label="<?php print(ExternalSearchPlaceholder);?>" aria-describedby="ext_search">
            <div class="input-group-append">
              <button class="btn btn-outline-secondary" type="submit" id="ext_search" name="submit" disabled>Search</button>
            </div>
          </div>
        <form>