YanoSec / Code
Predicted DOM trace for dom-demo.html. You can finish this card without opening the page or running the script. A file URL refers to the saved local document; reading it does not create an HTTP exchange.

Before a click:
element p, id status, text waiting
element button, id mark, text Mark ready

Click event on #mark runs the function in the script.
querySelector("#status") selects the paragraph whose id is status.
textContent replaces that paragraph's text with ready.

After the click, in this prediction:
status text: ready
No request leaves the browser.
No server account or permission changes.