Call a function in functions.php from within <script> tags (JS)

Question

I have a pretty simple problem (I think) which I can't find an answer to. The setup is pretty basic. I have a function which is in functions.php:

function function_A($variable)
{
    return $variable + 1;
}

In another php file I can call this function like this which works as expected:

   require_once(rtrim($_SERVER['DOCUMENT_ROOT'], '/') . '/wp-load.php');
   $result = function_A(5);

In a totally separate .php file I got lots of functions within <script> tags, and in one of them I want to access function_A from functions.php. Like this:

<script>
function problem_function(){
    // Here I want to call function_A and get the variable back to use in JS
}
</script>

I tried something like this which made the page fail to load:

<script>
function problem_function(){
    <?php
        require_once(rtrim($_SERVER['DOCUMENT_ROOT'], '/') . '/wp-load.php');
        $result = function_A(5);
    ?>
   
    var test = <?php echo $result; ?>;
}
</script>

How can I access function_A from a function within the <script> tag?