message Alert on an empty search

Hi experts, I wish to put message alert during search, once no item found upon searching. Codes below are working but I do not know  where to position an alert messages that would tell the user "No item". Thank you!

JavaScript:

var inp=function(){  
  var inputElem=document.getElementById("myInput");
  var buttElem=document.getElementById('myButton');
  var valueInput=inputElem.value;  
  return valueInput;
 };
  var table=function(){
  var tableElem=document.getElementById('myTable');  
  return tableElem;
};

function mySearch2(inpuArg, tableArg)
{
  var filter = inpuArg.toUpperCase();
  for(var i = 0; i < tableArg.rows.length; i++) {
    var tr = tableArg.rows[i];
    var cell = tr.cells[1];

    if (cell.textContent.substr(0,filter.length).toUpperCase() == filter) {
      tr.style.display = 'table-row';
    }
    else {
      tr.style.display = 'none';
      alert("no item");
    }
  }
}