ReactMarfeelAdserverProvider.js

import React from "react";
import ReactDOM from "react-dom";

class MarfeelAdserverProvider extends React.Component {
  render() {
    
    const adserverHtml = document
      .createRange()
      .createContextualFragment(
        '<ins class="adsense" slot="mySlot" clientId="myClientId"><h1>Adserver Type</h1>Adsense</ins>'
      );

    return fromHtmlElementToReact(adserverHtml.firstElementChild);
  }
}

function fromHtmlElementToReact(htmlElement) {
  if (isTextNode(htmlElement)) return htmlElement.data;

  return React.createElement(
    htmlElement.tagName, 
    getHTMLElementAttributesAsObject(htmlElement), 
    getHTMLElementChildrenAsReactComponents(htmlElement)
  );
}

function isTextNode(htmlElement) {
 return !(htmlElement instanceof HTMLElement);
}

function getHTMLElementAttributesAsObject(htmlElement) {
 const attributes = {};

  for (let i = 0; i < htmlElement.attributes.length; i++) {
    const attribute = htmlElement.attributes.item(i);
    attributes[attribute.name] = attribute.value;
  }
  
  return attributes;
}

function getHTMLElementChildrenAsReactComponents(htmlElement) {
  return  [...htmlElement.childNodes].map(child =>
    fromHtmlElementToReact(child)
  );
}

ReactDOM.render(
  React.createElement(MarfeelAdserverProvider, null, null),
  document.getElementById("root")
);