if( ! function_exists( 'themename_wp_enqueue_scripts' ) ){
    function themename_wp_enqueue_scripts() {
        /**
         * Do not add wp_enqueue_script( 'jquery' );
         * If the script requires jquery as below
         */
        wp_enqueue_script( 'themename-my-script', get_template_directory_uri() . '/assets/js/my-script.js', array( 'jquery' ), '1.0', true );

    }
    add_action( 'wp_enqueue_scripts' , 'themename_wp_enqueue_scripts' );
}