custom head examnple

custom-head.js

// custom-head.js (the file NEXT_PUBLIC_CUSTOMJS_HEAD points to)

// --- Google Tag Manager ---
(function(w,d,s,l,i){
  w[l]=w[l]||[];
  w[l].push({'gtm.start': new Date().getTime(), event:'gtm.js'});
  var f=d.getElementsByTagName(s)[0],
      j=d.createElement(s),
      dl=l!='dataLayer'?'&l='+l:'';
  j.async=true;
  j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;
  f.parentNode.insertBefore(j,f);
})(window,document,'script','dataLayer','GTM-NDRZTBJD');
// --- end GTM ---

// ... rest of your existing custom head JS ...