How to change a variable on a page without reloading?

Question

JavaScript

Good evening, today I wrote a parser that takes the dollar rate from a given source and writes it to a variable, I pass this variable to the template using Flask and it is displayed on the site, so {{ dollar }}, the question is, how can I do it so that the value displayed on the page changes in real time, and not after reloading the page?

Answer 1

Ajax

Answer 2

The simplest thing is to request an update from the server using Javascript via Ajax at some frequency (yes, at least once a second).
If you absolutely need to receive updates as they become available, you can use SSE or WebSockets, but here everything is already a little more complicated.
There is a presentation in English, which just describes all the methods and gives examples of server code for Flask.