Why do browsers send an OPTIONS preflight?
PICTURE THIS: A REST CALL
Simple meaning
Cross-origin requests with custom headers or methods trigger a CORS preflight.
WHY — HTTP instead of guessing?
Why interviewers care about HTTP:
on HTTP.
the situation, the default choice, and one exception - that reads as experience.
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:
- 1Cross-origin requests with custom
headers or methods trigger a CORS preflight.
- 2The server must allow
origin and headers.
- 3Missing OPTIONS handling breaks
the SPA while Postman still works.
- 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
Cross-origin requests with custom headers or methods trigger a CORS preflight. The server must allow origin and headers.