SOURCE

var xmlHttp=null;

function showHint(str)
{
if (str.length==0)
  { 
  document.getElementById("txtHint").innerHTML="";
  return;
  }
try
  {// Firefox, Opera 8.0+, Safari, IE7
  xmlHttp=new XMLHttpRequest();
  }
catch(e)
  {// Old IE
  try
    {
    xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
    }
  catch(e)
    {
    alert ("Your browser does not support XMLHTTP!");
    return;  
    }
  }
var url="/ajax/gethint.asp?q=" + str;
url=url+"&sid="+Math.random();
xmlHttp.open("GET",url,false);
xmlHttp.send(null);
document.getElementById("txtHint").innerHTML=xmlHttp.responseText;
}

<form>
   First Name: 
  <input type="text" id="txt1" onkeyup="showHint(this.value)"> 
 </form>
 <p>Suggestions: <span id="txtHint"></span></p>