React is not defined ReferenceError? I am using webpack and webpack-dev-server
<p>this is my <strong>jsx</strong>:  </p>

<pre><code> var React = require('react');
  var ReactDOM = require('react-dom');
  ReactDOM.render(
    &lt;h1&gt;hello world&lt;/h1&gt;,
    document.getElementById('content')
  )
</code></pre>

<p>I build with webpack to <code>build/bundle.js</code> &amp;<br>
I import <code>bundle.js</code> into <code>index.html</code>  </p>

<p><strong>index.html:</strong></p>

<pre><code>&lt;!DOCTYPE html&gt;
&lt;html&gt;
  &lt;head&gt;
  ┊ &lt;meta charset="utf-8"&gt;
  ┊ &lt;meta name="viewport" content="width=device-width"&gt;
  ┊ &lt;title&gt;&lt;/title&gt;
  &lt;/head&gt;
  &lt;body&gt;
  ┊ &lt;div id="content"&gt;&lt;/div&gt;
  ┊ &lt;script src="./build/bundle.js" type="text/javascript" charset="utf-8"&gt;&lt;/script&gt;
  &lt;/body&gt;
&lt;/html&gt;
</code></pre>

<p>But when I ran <code>webpack-dev-server</code>, chrome console error:<br>
<code>bundle.js:57 Uncaught ReferenceError: React is not defined</code><br>
I am sure, I have run <code>npm install react</code><br>
<a href="https://i.stack.imgur.com/2aXMx.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/2aXMx.png" alt="enter image description here"></a></p>

<p>how can I fix it?(-_-)ゞ゛</p>