title: Extending an interface in TypeScript
body: <p>In JavaScript, it is straight-forwardd to add functions and members to the <code>prototype</code> of any type. I'm trying to achieve the same in TypeScript as follows:</p>
  
  <pre><code>interface Date
  {
      Minimum: Date;
  }
  
  Date.prototype.Minimum = function () { return (new Date()); }
  </code></pre>
  
  <p>This produces the following error:</p>
  
  <pre><code>Type '() =&gt; Date' is not assignable to type 'Date'.
  Property 'toDateString' is missing in type '() =&gt; Date'.
  </code></pre>
  
  <p>Considering TS is strongly-types, how could we achieve this?</p>
  
  <p>Since I'm writing a custom utility library in TS, I'd rather not resort to JS.</p>