title: Adding existing functions in TypeScript: Node.getAttribute()
body: <p>What is the best way to add a function to typescript that actually exists already? In my case this is <code>Node.getAttribute()</code>, which is actually built-in to the browser, but not yet recognized by TypeScript. It errors: <code>Cannot find property 'getAttribute' on type 'Node'.</code></p>
  
  <p>In my case I ran into this error executing the following:</p>
  
  <pre><code>var xmlDocument = new DOMParser().parseFromString(xmlString, "text/xml"),
      rootfile    = xmlDocument.getElementsByTagName("aNode")[0];
  
  console.log(rootfile.getAttribute("anAttribute"));
  </code></pre>
  
  <p>This succeeds in the browser, but throws an error by TypeScript. </p>