If jQuery is hardcoded into your theme files this may cause plugins that rely on jQuery to break as reloading the jQuery library a second time overwrites previously loaded jQuery plugin files.
To avoid this you can add jQuery via your functions.php file using a built-in WordPress function. This will coordinate between all of the files that require the library to ensure that only one version is loaded. The default code below will load jQuery from the version that is packaged with the WordPress core files.
Add the following code to functions.php:
add_action('template_redirect','custom_theme_files');
function custom_theme_files() {
wp_enqueue_script( 'jquery' );
}
Hopes this helps
