I want to allow an editor to paste in the Google Ad Manager code into and extrafield which gets added to the HEAD.

When I try the following I get (0 - Call to a member function addScriptDeclaration() on null)

<?php
$doc->addScriptDeclaration('<?php echo $this->item->extraFields->HEADCODE->value ;?>');
?>

This is the code in the EF:
<script async src="securepubads.g.doubleclick.net/tag/js/gpt.js">
<script>
window.googletag = window.googletag || {cmd: []};
googletag.cmd.push(function() {
googletag.defineSlot(\'/21745156823/i10_sidebar_1\', [300, 250], \'div-gpt-ad-1587755337037-0\').addService(googletag.pubads());
googletag.pubads().enableSingleRequest();
googletag.enableServices();
});
</script>

If this is possible, can you help me with the correct method to accomplish this?

Awesome thanks! I made it JFactory instead and it works great!

I can create a separate post if you want but this is also part of this custom setup.

When I put:
{source}<?php echo $this->item->extraFields->adcode->value ;?>{/source}
into a the content area of an item, I get:
0 - Using $this when not in object context

Is there a solution for this?

www.icd10monitor.com/google-ads-test?google_preview=Xnc7DpJNPq0YnpWc9QUwnrHR_AWIAYCAgKDnoY28gwE&iu=21745156823&gdfp_req=1&lineItemId=5311773287&creativeId=138304104308

I was able to solve this by using RegularLabs Articles Anywhere and this code: {article type="k2"}[extra-22]{/article}