title: Express update a certain html field
body: <p>I have created a simple page that you login with a service and it gets the accounts username using nodejs. I then give the user a file that look like this:</p>
  
  <pre><code>&lt;html&gt;
  &lt;body&gt;
  &lt;p&gt;Hello &lt;span id="user"&gt;user-placeholder&lt;/span&gt;&lt;/p&gt;
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>Index.js: (assume user is logged in as they are)</p>
  
  <pre><code>app.get('/authorized', functiong(req,res){
      console.log(accountInfo.username);
      res.sendFile(file);
  });
  </code></pre>
  
  <p>I just want to update the <code>span</code> that has id <code>user</code> with <code>accountInfo.username</code>. 
  I'm not sure how exactly to update this value.</p>