title: how to do i get trunc day date
body: <p>i want to get the trunc date with such format : </p>
  
  <blockquote>
    <p>20190326</p>
  </blockquote>
  
  <p>this code in my schema :</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code> dateCreated: {
       
          type: Date,
          default: Date.now
      }</code></pre>
  </div>
  </div>
  
  gives the following result :</p>
  
  <blockquote>
    <p>2019-03-26T01:05:43.778Z</p>
  </blockquote>