title: TS2349: Cannot invoke an expression whose type lacks a call signature
body: <p>I know this issue is covered in other posts but I still can't figure out how to make this work - I'm getting the error:</p>
  <p><code>TS2349: Cannot invoke an expression whose type lacks a call signature. Type 'string | Function' has no compatible call signatures.</code></p>
  <p>The console logs a function but I can't call it.</p>
  <p>Here is my code:</p>
  <pre class="lang-js prettyprint-override"><code>const func = (): string =&gt; 'hi';
  
  const array: (string | Function)[][] = [['string', func]];
  
  const response = array[0][1];
  
  console.log(response); // ƒ () { return 'hi'; }
  
  response(); // TS2349: Cannot invoke an expression whose type lacks a call signature. Type 'string | Function' has no compatible call signatures
  </code></pre>