Link GA tracking example

Create a file named CustomLink.php in mysite/code

<?php

class CustomLink extends DataExtension
{

    private static $db = array(
        'TrackingLabel' => 'varchar'
    );

    public function updateCMSFields(FieldList $fields)
    {
        $fields->addFieldsToTab(
            'Root.Main',
            array(
                TextField::create(
                    'TrackingLabel',
                    'Tracking label'
                )
            )
        );
        return $fields;
    }

    public function getTrackingAttr()
    {
        if($this->owner->TrackingLabel){
            return " data-ga-label='$this->owner->TrackingLabel' ";
        }
    }

In your config.yml

...
Link:
  extensions:
    - CustomLink
...

Create a file named Link.ss in theme directory

<a href='{$LinkURL}'{$TargetAttr}{$ClassAttr}{$TrackingAttr}>
    {$Title}
</a>

Add the following script in your theme js

$(document).ready(function() {
    $('[data-ga-label]').each(function(){
        $(this).on('click', function() {
            var $trackingName = $(this).data('ga-label');
            ga('send', 'event', 'button', 'click', $trackingName);
        });
    });
});