Accepted answer

ReactDOM available since version 0.14.0, so you need to use React.render (because you have a React version 0.13.3) instead,

setInterval(function() {
    <HelloWorld date={new Date()} />,
}, 500);

or upgrade your React version and include ReactDOM

Changes in React 0.14


To make it work properly, you have to do 3 things.

  1. Import the CDNs, necessary for the developement(Say react and react-dom for web development)
<script crossorigin src=""></script>
  1. install babel-cli . It is needed for the compilation of JSX into vanila js

  2. change the typo in your code,

it is ReactDOM , not RaactDOM


Make sure it's ReactDOM (case sensitive)
          class App extends React.Component {
            render() {
                return (
                        <div className="commentbox">Hello React ! </div>
        ReactDOM.render(<App />, document.getElementById('root'));


Make sure that you've included react-dom.js. You can add it from CDN or use js toolchain of your choice.

Installing React - using a CDN

<script src=""></script>
<script src=""></script>


You have to import it

import ReactDOM from 'react-dom';


It may be the spelling issue - it is ReactDOM, not ReactDom.

This has changed over time with the new release of React

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