I’m trying to use Google Analytics to track events when users click on the button. How do I add the code correctly? I tried this but it doesn’t work.

[button href="http://testing.com" rel="nofollow" target="_blank" onClick="ga('send', 'event', { eventCategory: 'affiliate', eventAction: 'vendorname'});" css_classes="button_hilite _button"]Get More Details[/button]

function shortcode_boc_button($atts, $content = null){

	$atts = shortcode_atts(
			array(
				'css_classes' => '',
				'href' => '',
				'target' => '',
			), $atts);	
	$target = ($atts['target'] ? " target='".$atts['target']."'" : '');
    return '<a href="'.$atts["href"].'" class="button '.$atts["css_classes"].'" '.$target.'>'.do_shortcode_boc($content).'</a>';  
}

Let’s add the new param, say onclick:

function shortcode_boc_button($atts, $content = null){

	$atts = shortcode_atts(
			array(
				'css_classes' => '',
				'href' => '',
				'target' => '',
				'onclick' => '',
			), $atts);	
	$target = ($atts['target'] ? " target='".$atts['target']."'" : '');
        $onclick = ($atts['onclick'] ? " onclick=\"".$atts['onclick']."\"" : '');

    return '<a href="'.$atts["href"].'" $onclick class="button '.$atts["css_classes"].'" '.$target.'>'.do_shortcode_boc($content).'</a>';  
}

Now try your code like so:

[button href="http://testing.com" rel="nofollow" target="_blank" onClick="ga('send', 'event', { eventCategory: 'affiliate', eventAction: 'vendorname'});" css_classes="button_hilite _button"]Get More Details[/button]

and let me know if it works for you.