jQuery for smooth scrolling to top of page.

enqueue-core.php

<?php
//* Do NOT include the opening php tag

//* Add Core JS file
add_action( 'wp_enqueue_scripts', 'b3m_add_core_js' );
if ( ! function_exists( 'b3m_add_core_js' ) ) {
	function b3m_add_core_js() {
		wp_enqueue_script( 'core-js', get_stylesheet_directory_uri() . '/lib/js/core.js', array('jquery'), '1.0.0', true );
	}
}

smooth-scroll-link.html

<!-- Create a hyperlink and assign it the class 'smooth-scroll' -->
<a class="smooth-scroll" href="#" title="top of page" rel="nofollow">Top of Page</a>

smooth-scroll.js

//* Smooth scrolling
jQuery(document).ready(function() {
        var duration = 800;
        jQuery('.smooth-scroll').click(function(event) {
            event.preventDefault();
            jQuery('html, body').animate({scrollTop: 0}, duration);
            return false;
        })
});