Using header() with wordpress enqueue

I’m basically trying to make my js and css files dynamic. I’ve tried a few different ways of doing this and it isn’t seeming to work for me. Any help would be greatly appreciated!

functions.php

function fnp_add_js() {
    //I've tried fnp_jquery.js.php fnp_jquery.php and fnp_jquery.js
    wp_register_script( 'fnp_jquery', plugins_url( 'fnp_jquery.js.php', __FILE__ ));

    wp_enqueue_script('fnp_jquery');
}

base.php

add_action('wp_enqueue_scripts', 'fnp_add_js');

jquery.js
(I’ve tried fnp_jquery.js.php fnp_jquery.php and fnp_jquery.js)

<?php 
header('Content-type: text/javascript');

//I've also tried surrounding $(document).ready(function() {}  with echo ''; 
?>

$(document).ready(function() {
   //Javascript here
});