Dynamic changing variables without reloading page (Python Flask and HTML)

I'd like to ask you how to change variables on HTML using Python Flask dynamically. For example, I'd like to change list of messages in chat, so I have this in my Python code to render page

    return flask.render_template('chat.html',
                             messagelist=app.messages)

and then this HTML code

<h2>Messages</h2>
    <hr>
    

    <h2>New message</h2>

Is there a way, how to update the list messagelist without user's interaction (refresh, HTTP method,... ) ?

Thank you