What is a union type?
PICTURE THIS: 1, 2, 2, 8
Simple meaning
A union means a value can be one of several types, like string or number, or loading or success or error.
WHY — TypeScript instead of guessing?
Why interviewers care about TypeScript:
who only read docs from people who shipped.
and tied to Frontend work.
Name the idea, why it exists, then one short example.
End with when you use it and one common pitfall.
STEPS — What happens step by step?
Before you speak the answer, walk the interviewer through these steps:
- 1A union means a
value can be one of several types, like string or number, or loading or success or error.
- 2I narrow with typeof
or a discriminant field before I use the data.
- 3That is how I
type API states without any.
- 4Give an example
One tiny concrete case you can say aloud.
- 5Common mistake
What juniors usually get wrong.
- 6Close
When you pick this over the alternative.
EXAMPLE — See it in action
Here's a short line you can speak, broken into clear beats:
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
A union means a value can be one of several types, like string or number, or loading or success or error. I narrow with typeof or a discriminant field before I use the data.