title: VueJs search form issue
body: <p>Here is an <a href="https://codepen.io/iTaurus85/pen/MqrqWj" rel="nofollow noreferrer">example</a> from the book "The Majesty of Vue", it works fine. But I was trying to make the code shorter and failed.</p>
  
  <p>So in the computed properies there is a function: </p>
  
  <pre><code>search: function(){
      var query = this.query
      return this.stories.filter(function(story){
        return story.plot.includes(query)
      });
  </code></pre>
  
  <p>I tried to remove <code>var query = this.query</code> and add directly to <code>return story.plot.includes(this.query)</code>. But this way it doesn't work. 
  Why? Isn't it the same?</p>