How to add an extra classname on iframe, generated by DFP?

I have a DFP creative template that needs to work both on old and new site. So on the new site (which has its own advertisement component js), I'd like to add a classname "redesign" on the DFP iframe. How do I do it properly?

In conclusion, I'd like to have same creative template on DFP with extra classname for new site.

Solution

Solved it by using the plugin => https://github.com/mcountis/dfp-events

So on redesign ad.js component, I add a new classname "redesign".


    window.googletag.cmd.push(function() {
        window.googletag.on('gpt-slot_rendered', function(e,level,message,service,slot) {
            var slotId = slot.getSlotId();
            var $slot = $('#' + slotId.getDomId());

            // DFP adds two iframes, one for calling scripts and one for displaying the ad. we want the one that is not hidden
            if ($slot.find('iframe:not([id*=hidden])')
                .map(function() { return this.contentWindow.document; })
                .find('body')
                .children().length > 0
            ) {
                $slot.find('iframe').contents().find('body').addClass('redesign');
            }
        });
    });