A structured lesson workspace with readable content, hands-on examples, and a clean path to completion.
| Question to ask | Good diagnostic move |
|---|---|
| What value entered? | Inspect the runtime value and type. |
| What rule applied? | Check the construct's language or host semantics. |
| What changed? | Compare the smallest working and failing cases. |
const result = Promise.resolve(21).then(value => value * 2).catch(error => console.error(error));result.then(console.log);
<strong>Core idea:</strong> Debugging is a reasoning process: observe the failure, form a hypothesis, inspect the runtime state, then make the smallest useful change. In this lesson, the practical target is debugging asynchronous javascript: you should be able to predict what the runtime will do before changing the code.
<strong>Core idea:</strong> Debugging is a reasoning process: observe the failure, form a hypothesis, inspect the runtime state, then make the smallest useful change. In this lesson, the practical target is debugging asynchronous javascript: you should be able to predict what the runtime will do before changing the code.
Mentor note: for debugging asynchronous javascript, 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.