While I'm learning JavaScript, I started to work on the following example


The script sends an Ajax call and gets back a simple JSON file.
I fetch the response and build a simple unordered list using Handlebars.js.
So far so good.

Now I wanted that if I click on the button in front of each character, a hidden div becomes visible, which contains some details about the character.
I achieved this easily using jQuery.
However, I spent a whole day to convert that small jQuery snippet to vanilla JS and failed badly. :-(

How can I change the jQuery snippet, which shows and hides the div to vanilla JS?
It's not important if it slides or not. It would be enough if I could just show and hide it by adding the class visible to it.

This is the jQuery code, I want to convert to vanilla JS:
// jQuery solution using event delegation for slideToggle
$('#container').on('click', 'button.btn', function() {
  console.log($(this)); // this is the button with the class btn

  // If the button is clicked, add a class to .details