How to insert a hardcode javascript in head tag of the HTML DOM

insert_hardcode_javascript_in_head_tag_dom.html

<script type="text/javascipt">
  try{
    (function(window,document){
      head=document.getElementsByTagName('head')[0];
      script=document.createElement('script');
      // treat the hardcode script tag
      head.appendChild(script);
    })(window,document);
  } catch(e) {
    console.log('[GTM][Error in tag "nomeDaTag"]: '+e);
  }
</script>