title: If a strict mode function is executed using function invocation, its 'this' value will be undefined
body: <p>I'm getting the following warning when using <a href="http://jshint.com/" rel="nofollow noreferrer">jshint</a>.
  Why?</p>
  
  <blockquote>
    <p>If a strict mode function is executed using function invocation, its 'this' value will be undefined.</p>
  </blockquote>
  
  <pre><code>function demo() {
      'use strict';
  
      document.querySelector('#demo').addEventListener('click', test);
  
      function test() {
          console.log(this);
      }
  }
  </code></pre>