Ajaxify calendar

Write your required javascript, then use this code to display it on the page, it ensures that the script is only included if the calendar is displayed

add_filter('get_calendar',  'add_calendar_scripts');
function add_calendar_scripts($content) {
    add_action( 'wp_footer', 'output_calendar_scripts', 11);
    return $content;
}

function output_calendar_scripts() {
    ?>
    <script type="text/javascript" src="https://wordpress.stackexchange.com/questions/70078/<?php echo get_template_directory_uri();?>/path/to/script.js"></script>
    <?php
}