I can not run JavaScript file in ajax Call

I can not run JavaScript file in ajax Call

Hi Dears.

my code is like this :

Html Code :


<html>
<head>

<script src="jquery.js"></script>

<script>

function showHint(str)
{
if (str.length==0)
  { 
  document.getElementById("usa").innerHTML="";
  return;
  }
var xmlhttp=new XMLHttpRequest();
xmlhttp.onreadystatechange=function()
  {
  if (xmlhttp.readyState==4 && xmlhttp.status==200)
    {
    document.getElementById("usa").innerHTML=xmlhttp.responseText;
    }
  }
xmlhttp.open("GET","a.php" ,true);
xmlhttp.send();
}

</script>

</head>

<body>
<div id="usa">

<img src="image/d2.jpg" onmouseover="omid(this)" />

</div>
</body>

</html>







and PHP code is :


<html>
<head>

<script src="jquery.js"></script>


</head>

<body>

<?php
echo "<h1 id='usa'>Salam Omid php</h1>";
echo '<script>
$("#usa").click(function(){
$.getScript("alert.js");
});
</script>';
?>

</body>
</html>






JS file:


alert ("hello");




when I run a.php the alert.js will run but when I call a.php using ajax، the javascript file in php file will not run.

how can i run java script file that are in another files ?

thanks.