素のjavascriptでセレクトのフィルタリングを行う実装

<script>
var original = new Array();
function filterSelect(obj) {
 // fword → filtered wordの略な
 var fword = obj.value;
 var sel = document.getElementById("target");
 if (original.length == 0) {
  for (var i=0; i < sel.options.length; i++) {
   original[sel.options[i].value] = sel.options[i].text;
  }
 }
 // remove options
 sel.length = null;
 // create new options
 for (var key in original) {
  if (original[key].indexOf(fword) >= 0) {
   var newOpt = document.createElement( "option" );
   newOpt.value = key;
   var optTxt = document.createTextNode( original[key] );
   newOpt.appendChild( optTxt );
   sel.appendChild( newOpt );
  }
 }
}
</script>
<input type="text" onkeyup="filterSelect(this)">
<select id="target">
<option value="1">abcde</option>
<option value="2">cdefg</option>
<option value="3">fghij</option>
<option value="4">jklmn</option>
<option value="5">lmnopq</option>
<option value="6">acfjl</option>
</select>

<script> var original = new Array(); function filterSelect(obj) { // fword → filtered wordの略な var fword = obj.value; var sel = document.getElementById("target"); if (original.length == 0) { for (var i=0; i < sel.options.length; i++) { original[sel.options[i].value] = sel.options[i].text; } } // remove options sel.length = null; // create new options for (var key in original) { if (original[key].indexOf(fword) >= 0) { var newOpt = document.createElement( "option" ); newOpt.value = key; var optTxt = document.createTextNode( original[key] ); newOpt.appendChild( optTxt ); sel.appendChild( newOpt ); } } } </script> <input type="text" onkeyup="filterSelect(this)"> <select id="target"> <option value="1">abcde</option> <option value="2">cdefg</option> <option value="3">fghij</option> <option value="4">jklmn</option> <option value="5">lmnopq</option> <option value="6">acfjl</option> </select>