title: Check if a variable is of "async function" type
body: <p>Given a variable, which is defined as follows:</p>
  
  <pre><code>const f = async function() {/* ... */};
  </code></pre>
  
  <p>How can I check if the variable <code>f</code> is of type <code>async function</code> ?</p>
  
  <p>I already found this solution:</p>
  
  <p><code>f.constructor.name === "AsyncFunction";</code></p>
  
  <p>But the "f.constructor.name" is not compatible with IE11. Any other ideas ?</p>
  
  <p>I know async functions does not work in IE11, ... but they work through babel compilation process. The idea is to find a way to detect async functions in an environment like node.js which would be compatible with IE11/babel for instance</p>