title: babel-core: Uncaught TypeError: Cannot read property 'keys' of undefined
body: <p>This is my <code>index.html</code>:</p>
  
  <pre><code>&lt;!DOCTYPE html&gt;
  &lt;html lang='ru'&gt;
  &lt;head&gt;
    &lt;meta charset='utf-8'/&gt;
    &lt;title&gt;Sandbox&lt;/title&gt;
    &lt;script src='https://cdnjs.cloudflare.com/ajax/libs/babel-core/6.1.19/browser.min.js'&gt;&lt;/script&gt;
    &lt;script src='js/index.js' type='text/babel'&gt;&lt;/script&gt;
  &lt;/head&gt;
  &lt;body&gt;
    &lt;div id='foo'&gt;&lt;/div&gt;
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>This is my <code>js/index.js</code> file:</p>
  
  <pre><code>"use strict";
  
  window.onload = function(){
    const stuff = () =&gt; document.getElementById('foo').textContent = 'Hello!'
    stuff()
  }
  </code></pre>
  
  <p>I get the error in Google Chrome v64.0.3282.140 when I open my HTML-file:</p>
  
  <p><a href="https://i.stack.imgur.com/YkNWk.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/YkNWk.png" alt="enter image description here"></a></p>
  
  <p>Why does it happen?</p>