title: TypeScript Property 'forEach' does not exist on type 'FileList'
body: <p>I enable users to upload multiple files. Then I need to iterate over these files and perform some actions. I wanted to add some extra functionality to <code>FileList</code> but TS does not know <code>forEach</code> on <code>FileList</code> arrays. This is my code:</p>
  
  <pre><code>public uploadMultiple(evt){
      console.log(evt.files);
      FileList.prototype.forEach = function(callback) {[].forEach.call(this, callback)};
  }
  </code></pre>