title: How to add a class to an element in an HTML string without using JQuery
body: <p>I have an html string that looks like this :</p>
  
  <pre><code>'&lt;p&gt;Hello&lt;/p&gt;&lt;p&gt;I would like to schedule a meeting with you.&lt;/p&gt;
   &lt;a class="button button--blue" href="#"&gt;
     &lt;button class="button 
        button--blue"&gt;Schedule meeting
     &lt;/button&gt;
   &lt;/a&gt;
   &lt;p&gt;See you soon.&lt;/p&gt; 
   &lt;p&gt;baher&lt;/p&gt;',
  </code></pre>
  
  <p>How can i access these elements individually to add a class to them without using jQuery?
  please note that i'm working on the server side so stuff like <code>document</code> and <code>window</code> are not accessible </p>