How to use Ajax to inject specific PHP function using URL, or other method?

I'm moving from the realm of just JS to php and Ajax. I've dabbled some with PHP in the past. I really appreciate how much help stackoverflow has been in helping me with basic questions.

let says I have a div called #divName.

I use the following JS for Ajax. Some of this is just pseudo code.

var request = false;
   try {
     request = new XMLHttpRequest();
   } catch (trymicrosoft) {
     try {
       request = new ActiveXObject("Msxml2.XMLHTTP");
     } catch (othermicrosoft) {
       try {
         request = new ActiveXObject("Microsoft.XMLHTTP");
       } catch (failed) {
         request = false;
       }  
     }
   }

   if (!request)
     alert("Error initializing XMLHttpRequest!");

   function getAjaxInfo(<name of the php function???>) { //<<<<< this is the function I need help with
    var myFunction= nameOfPHPfunctionIJustGot;
     var url = "filename.php?func=" + myFunction;
     request.open("GET", url, true);
     request.onreadystatechange = updatePage;
     request.send(null);
   }

  function updatePage() {
     if (request.readyState == 4) {
     开发者_Go百科  if (request.status == 200) {
         var response = request.responseText;
             document.getElementById("divName").innerHTML = response; //probably going to use Jquery append here, but this example works.
               } else
         alert("status is " + request.status);
     }
   }

The I have my fileName.php file:

<?php

function header() { ?>
   header content goes here
<?php }

function footer() { ?>
    footer content goes here
<?php }

?>

My goal is that when I execute getAjaxInfo(), I can pull whatever PHP function I want.

So lets say if I do a onClick="getAjaxInfo(header)" it will get the php header function, apply it to a javascript function, and then apply that to a div.

Any help would be appreciated!

Try with:

$func=$_GET['func'];
if(function_exists($func)) $func();

In this way you get the function name passed by GET and the execute it.

If you want to be able to call only certain functions:

$allowedFunctions=array("header","footer");
$func=$_GET['func'];
if(in_array($func,$allowedFunctions) && function_exists($func)) $func();

Picking up on @VolkerK's suggestion, and adding a failure function:

$func = $_GET['func'];
$allowed = array('header', 'footer');
if (in_array($func, $allowed) && function_exists($func)) $func();
else default_action();

<?php

$allowedFunctions = array(
   'header',
   'footer'
);

$functionName = $_GET[ 'func' ];

if( in_array( $functionName, $allowedFunctions ) && function_exists( $functionName ) )
{
    $functionName();
}

/* your function definitions */
?>

$allowedFunctions is a whitelist array of user defined (i.o.w. your) php functions that you want the ajax call to allow to execute. If you don't keep this whitelist, your script will be potentially dangerous, since it would allow anyone to execute an arbitrary function. That is something you definately do not want.