Browser & Web Performance · Senior · Question 43 of 75

Why do preflights hurt performance in an API-heavy SPA, and how can you reduce them?

✓Correct answer: Each non-simple cross-origin request may need an extra OPTIONS round trip; use the same origin (e.g. a proxy path) or a long Access-Control-Max-Age
2Preflights block rendering; load them with defer
3Preflights download the API schema; disable it in fetch options

Explanation

Serving the API under the app's origin (/api) removes CORS entirely. Preflight caching is per URL and capped by browsers.

Further reading

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