How to detect if an HTML Element is the root of a React Component?

Question

Is there a way to detect if an HTML Element is the root of any React component in a production app?

I'm not referring to detecting wether an element is the root of the entire React application, rather detecting if an element is the root of any component.

To illustrate:

Let's say we have the following React components:

const FooBar = () => {
  return (
    <div className="foobar">
      <span> foo </span>
      <button> bar </button>
    </div>
  );
}

const Container = () => {
  return (
    <div>
      <a className="john"> john </a>
      <a> doe </a>
      <FooBar />
    </div>
  );
}

That transpiles to the following HTML:

<div>
  <a class="john"> john </a>
  <a> doe </a>
  <div class="foobar">
    <span> foo </span>
    <button> bar </button>
  </div>
</div>

In a production deployment, is there a way to do this from a chrome extension (external script)? and how?

const foobarDiv = document.querySelector('div.foobar');
const span = document.querySelector('span');
const a = document.querySelector('a.john');
isReactComponentRoot(foobarDiv); // true
isReactComponentRoot(span); // false
isReactComponentRoot(a); // false

Answer 1

I don't know if this will continue to be reliable in the future, but something that's worked for a while is to check if it has a _reactRootContainer property.

const root = document.querySelector('.react');
const App = () => {
    return <div className="child"></div>;
};

ReactDOM.render(<App />, root);

console.log(root.hasOwnProperty('_reactRootContainer'));
console.log(root.querySelector('.child').hasOwnProperty('_reactRootContainer'));

<script crossorigin src="https://unpkg.com/react@16/umd/react.development.js"></script>
<script crossorigin src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script>
<div class='react'></div>