title: What happens if polyfill script fails to download?
body: <p>I have a SPA (built on webpack, with babel, etc) that includes a polyfill in the index.html:</p>
  
  <pre><code>&lt;script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=Promise,Array.prototype.includes,Element.prototype.remove"&gt;&lt;/script&gt;
  </code></pre>
  
  <p>One use-case for the polyfill is in order to use the Promise API on IE 10-11.</p>
  
  <p>My error monitoring reporting an error on an IE 11 client of the following:</p>
  
  <pre><code>ReferenceError: 'Promise' is undefined
  </code></pre>
  
  <p>So I assume that particular session failed to download the polyfill for some reason.</p>
  
  <p>My question is: How should I deal with this case? Is it a scenario I should expect to happen sometimes? Is the user expected to noticed the application not working properly, and reload the page?</p>