React: How to inject React component into body?

Create the root element and append it to the DOM yourself

const rootEl = document.createElement('div')

document.body.appendChild(rootEl)


class Root extends React.Component {
  render () {
    return <div>heyyyyyyy</div>
  }
}

ReactDOM.render(
  <Root />,
  rootEl
)
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>

<div>don't replace me</div>

If you opt for a one-liner :

ReactDOM.render(
  <Root />,
  document.body.appendChild(document.createElement("DIV"))
)

Running Example:

class Root extends React.Component {
  render() {
    return <div>It works!</div>;
  }
}

ReactDOM.render(
  <Root />,
  document.body.appendChild(document.createElement("DIV"))
)
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.0.0/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.0.0/umd/react-dom.production.min.js"></script>

<body></body>