Events
addEventListener — click and live input.
Waiting for input…
DOM manipulation
Create, append, and toggle classes / styles at runtime.
List state (add / remove)
Hold an array in memory and re-render on change.
Form validation
Validate on submit; show inline feedback.
Timers
setInterval / clearInterval — a live player counter.
218 online
Fetch (async / await)
Simulated server-status request with a Promise.
Idle.
localStorage
Persist a preference across reloads (scoped to this page).
Array methods
map, filter, reduce over the live servers.
JSON
JSON.stringify / parse round-trip.