Q34. Why should catch errors be unknown?
JavaScript permits throwing arbitrary values, so a catch variable cannot safely be assumed to be an Error. Narrow with instanceof Error or validate the expected shape before reading properties. Handle non-Error thrown values deliberately.
An Error instance has a message property, but a thrown string or arbitrary object may not follow that shape.
Note
Interview approach: define the concept, explain why it matters, then mention one trade-off or limitation.
TypeScript concept
// Illustrative TypeScript contract
type Identifier = string;
const id: Identifier = "item-1";💡 The example demonstrates the compile-time contract discussed in this question.
Key Takeaways
- Explain the concept in your own words.
- Know the practical trade-off and its limits.
- Use a small example to demonstrate the idea.
Knowledge Check
What is a safe first check before reading `error.message`?