FrontendHaltBrowser internals·Intermediate·Conceptual·1 min read
What triggers a CORS preflight request?
Short interview answer
A request becomes non-simple, and therefore preflighted with OPTIONS, when it uses a method beyond GET/HEAD/POST, includes custom headers, or uses a content type such as application/json. The browser confirms permission before sending the real request.
Key takeaway
Explain the underlying mental model clearly, then support it with a concrete example and its trade-offs.