Q08. What is a discriminated union?
A discriminated union is a union of object types sharing a property whose literal value identifies the variant. Switching on that property narrows the object and supports exhaustive handling. It is useful for async states, commands, events, and API results.
A status field with loading, success, and error variants lets each case require the fields appropriate to that state.
Note
Interview approach: define the concept, explain why it matters, then mention one trade-off or limitation.
Discriminated union
type Result = { ok: true; data: string } | { ok: false; error: string };💡 The literal ok property identifies the variant.
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
Which field most commonly distinguishes variants in a discriminated union?