Understanding CORS: When Cross‑Origin Requests Are Executed, Intercepted, and Preflighted

This article explains the mechanics of CORS, detailing how browsers decide whether a cross‑origin request is executed directly, blocked, or preceded by a preflight OPTIONS request, and distinguishes between simple and complex requests based on method, headers, and other criteria.

CORSCross-OriginSimple Request

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Understanding CORS: When Cross‑Origin Requests Are Executed, Intercepted, and Preflighted

360 Tech Engineering

Sep 9, 2019 · Frontend Development

Understanding Simple and Preflight Requests in CORS

The article explains why CORS distinguishes between simple requests—limited to GET, HEAD, POST with specific headers and content types—and preflighted requests, describing the server‑side rationale, the mechanics of preflight, and why avoiding preflight for simple requests simplifies cross‑origin interactions.

CORSHTTPSimple Request

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Understanding Simple and Preflight Requests in CORS