Google Custom Search placeholder function in JavaScript
So after testing it,  you don't really need to define it in your javascript. You can simply add it in your HTML before all your other scripts.

That's what s.parentNode.insertBefore(gcse, s); does. It finds the first occurence of a script tag in your HTML (which is kind of funny as it won't work if there are no script tags in your HTML), and adds your new script before it.

So if the first occurence of a script tag appears in the HEAD, then it'll be placed in the head'



&lt;script src="https://cse.google.com/cse.js?cx=017643444788069204610:4gvhea_mvga" async type="text/javascript"&gt;&lt;/script&gt;
&lt;gcse:search&gt;&lt;/gcse:search&gt;




Making your javascript more efficient will be difficult as 1. there isn't much happening and 2. it's already very short.

But you could do something like this (which doesn't change much)... 

// google search placeholder
(function(cx) {   
    const gcse = document.createElement('script');
    gcse.type = 'text/javascript';
    gcse.async = true;
    gcse.src = `https://cse.google.com/cse.js?cx=${cx}`;
    const s = document.getElementsByTagName('script')[0];
    s.parentNode.insertBefore(gcse, s);
})('!!!!!!!!!!!!!!!!!!!');