To enqueue a JavaScript file in WordPress, you use the wp_enqueue_script function in your theme’s functions.php file.

Place the following code towards the top of your child theme’s functions.php document.

<?php
function custom_scripts() {
    // register and enqueue the script like this for a theme:
    wp_enqueue_script( 'my-theme-script', get_template_directory_uri() . '/js/custom-script.js', array(), '1.0.0', true );

    // if you need to add jQuery as a dependency, you can do it like this:
    wp_enqueue_script( 'my-theme-script', get_template_directory_uri() . '/js/custom-script.js', array('jquery'), '1.0.0', true );
}
add_action( 'wp_enqueue_scripts', 'custom_scripts' );
?>