A structured lesson workspace with readable content, hands-on examples, and a clean path to completion.
| Observation | Diagnostic question |
|---|---|
| Runtime value | What value actually arrived? |
| Language rule | Which rule determines the result? |
function parsePort(value) {const port = Number(value);if (!Number.isInteger(port) || port < 1 || port > 65535) {throw new RangeError('Invalid TCP port');}return port;}
Keep the experiment focused on javascript errors and error types and change one assumption at a time.
Keep the experiment focused on javascript errors and error types and change one assumption at a time.
Mentor note: for javascript errors and error types, name the invariant you need before reaching for a clever shortcut. Clear state and explicit assumptions make later debugging much cheaper.
Finish the lesson once you have worked through the material. This awards ★ 20 XP.