Editing shortcodes to add functionality

I use a theme (DICE) that has not been updated in a loooong time. Until I can devote the time for a full site redesign, we will continue using DICE.

I am working on getting some dynamically-generated page content using PHP/ajax. The php function will be called from a button click. I have got it to work perfectly, assuming I use the <button onclick=”func()”> syntax, but the moment I attempt to go deeper and use the shortcode button that we use for all of the buttons on the site, the button quits working to call the function.

How could I make it so that this button shortcode would support that PHP/ajax/javascript onclick=func() argument?

<?php	
	
	function btp_button_shortcode($atts, $content = null)
	{
		extract( shortcode_atts( array(
			'href' 			=> '#',
		    'priority'		=> 'primary',
			'size'			=> 'small',
			'wide'			=> false,
			'title'			=> '',
			'linking'		=> 'default',					
			), $atts ) );
		
		if ( !strlen( $href ) || $linking == 'none') {
			return '';
		}
		
		/* Compose output */
		$out 	= '';
		$rel 	= '';
		$class  = '';
		
		$class .= 'button ' . $priority . ' ' . $size . ' ';
		$class .= $wide ? 'wide ' : '';
		
		switch ( $linking ) {			
			case 'lightbox':
				$rel .= 'prettyPhoto ';
				break;
			case 'new_window':	
			case 'new-window':
				$class .= 'new-window ';
				break;
			default:
				break;
		}	
		
		$out .= '<a class="' . esc_attr( $class ) . '" ';
		$out .= 'href="' . esc_url( $href ) . '" ';
		$out .= 'title="' . esc_attr( $title ) . '" ';
		$out .= 'rel="' . esc_attr( $rel ) . '"';
		$out .= '><span>' . esc_html( $content ) . '</span></a>';
				
		return $out;
	}
?>