Suggested way to allow others to plugin to my php script and change variable values?

Question

People want to use my Jquery plugin, but get a list of images from a database instead of a directory, which is the standard way the plugin works.

My Jquery plugin that uses the ajax() function to deliver & return data to a php script.

The php script pulls files from a directory with getdir(), adds those files to an array and assigns that array to a variable.

People have requested the ability to create that variable value themselves by generating it from a database (not just pulling files from a directory using scandir).

What is a good, secure way to do to allow others to replace a variable value inside my php script?

Ideally, I would like there to be a way where users can create their own script in a separate document (and they don't need to alter my document).

Here is a simplified example of my script:

HTML Document

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js"&gt;&lt;/script&gt;
 <script>
$.ajax({
    type: "POST",
    url: "example.php",
    cache: false,
    data: {
        foo: "some_directory",
            },
    success: function(html){
    alert(html);
    }
});
</script>

PHP Document

<?php

$foo = $_POST["foo"];
$foo = scandir($foo);
$foo = (explode(",",$foo)); // how can I allow others to change this variable value?
foreach ($foo as $a) {
    echo "<p>$a</p>";
}

?>

Answer 1

It sounds like you might want to look into writing an API.

Answer 2

Use event based programming. When it comes time to assign the variable, Detect whether a function called "onGetDirAssignVar" exists. If it does, call the function and accept it's results. If it doesn't, then follow the default path.

var $foo;
if (function_exists("onGetDirAssignVar")) {
  $foo = onGetDirAssignVar(params);
} else {
  $foo = array("first","second"); // how can I allow this value to be changed?
}

foreach ($foo as $a) {
    echo "<p>$a</p>";
}