title: How to define type for a function callback (as any function type, not universal any) used in a method parameter
body: <p>Currently I have type definition as:</p>
  
  <pre><code>interface Param {
      title: string;
      callback: any;
  }
  </code></pre>
  
  <p>I need something like:</p>
  
  <pre><code>interface Param {
      title: string;
      callback: function;
  }
  </code></pre>
  
  <p>but the 2nd one is not being accepted.</p>