title: using documentMode with typescript
body: <p>I check if the browser is ie by:</p>
  
  <pre><code>function isBrowserIE() {
    return window.document.documentMode;
  }
  </code></pre>
  
  <p>Typescript raises an error:</p>
  
  <blockquote>
    <p>Error TS2339: Property 'documentMode' does not exist on type 'Document'.</p>
  </blockquote>
  
  <p>This is due to the <a href="https://github.com/Microsoft/TypeScript/wiki/Breaking-Changes" rel="noreferrer">change</a> made in typescript compiler at version 1.5 : </p>
  
  <blockquote>
    <p>Properties documentMode, parentWindow, createEventObject are removed from type Document</p>
  </blockquote>
  
  <p>How can i get rid from the error?</p>