What is CORS preflight?
PICTURE THIS: A REST CALL
ClientGET /users/1
ServerFind row
JSON back200 OK
Simple meaning
Browsers send OPTIONS before some cross-origin requests.
WHY — HTTP instead of guessing?
Why interviewers care about HTTP:
HTTP questions separate people
who only read docs from people who shipped.
Keep it short, concrete,
and tied to Full Stack work.
Stay structured
Name the idea, why it exists, then one short example.
Close cleanly
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:
- 1Browsers send OPTIONS before
some cross-origin requests.
- 2Servers must allow methods
and headers.
- 3Misconfig shows as client
network errors.
- 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:
Say this line
“Servers must allow methods and headers.”
Break into beats
Serversmustallowmethodsandheaders
Speaking order
2987408337471632900
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
Browsers send OPTIONS before some cross-origin requests. Servers must allow methods and headers.