making script work only for specific class

the code below is for adding links to words, but it work for the whole html and broke it.
I want make it effect only on child “p”

.post-body p

the code :

<script>
//<![CDATA[
function linkWords(elem,words,links) {
  elem.innerHTML=elem.innerHTML.replace(
    RegExp('('+words.join(')|(')+')','gi'),
      function(){
        for (var i=1;i<arguments.length-2;i++)
          if (arguments[i])
            return '<a href="'+links[i-1]+'" rel="tag">'+arguments[0]+'</a>';
      }
  );
}

document.addEventListener("DOMContentLoaded", linkWords(document.body,
  ["أكشن","Signal.MD","خارق للطبيعة","سحر"],
  ["https://www.example.com/search/label/%D8%A3%D9%83%D8%B4%D9%86","https://www.example.com/search/label/Signal.MD","https://www.example.com/search/label/%D8%AE%D8%A7%D8%B1%D9%82%20%D9%84%D9%84%D8%B7%D8%A8%D9%8A%D8%B9%D8%A9","https://www.example.com/search/label/%D8%B3%D8%AD%D8%B1"]
 ));
 //]]>
</script>