title: Extending another TypeScript function with additional arguments
body: <p>Is it possible in <a href="/questions/tagged/typescript" class="post-tag" title="show questions tagged &#39;typescript&#39;" rel="tag">typescript</a> to define a function type and extend its argument list in another type (overloading function type?)?</p>
  <p>Let's say I have this type:</p>
  <pre><code>type BaseFunc = (a: string) =&gt; Promise&lt;string&gt;
  </code></pre>
  <p>I want to define another type with one additional argument <code>(b: number)</code> and the same return value.</p>
  <p>If at some point in the future <code>BaseType</code> adds or changes arguments this should also be reflected in my overloaded function type.</p>