使用ajax从html文件执行php代码

I am new to php development and I am stuck on something stupid : I want to execute a php script from my html page.

I do the following to do so :

    $.ajax({
        type: "GET", 
        url: "test1.php",
        success: function(response) {
            //alert(response);
            console.log(response);
        },

        error: function(response) {

        }
    });

But when I log the response, I see the php source code in the response :

[Log] <?php  (localhost, line 23)
  $output = "LALALALALALALALALALALALALA"
  echo $output;
?> 

Try this ... call in head tag

<head>
 <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js"></script>
 <script src="https://ajax.googleapis.com/ajax/libs/jqueryui/1.8.18/jquery-ui.min.js" type="text/javascript"></script>
</head>  

in javascript tag

$.ajax({
                type: "GET",
                url: "test1.php",
                success: function (html) {
console.log(response);
                },

        error: function(response) {

        }
            });
        return false;