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CORS Preflight

طلب CORS التمهيدي

IntermediateAPIs & Integration1 min read
cors-preflightoptions-request
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Definition

Browser's automatic OPTIONS request to check if a cross-origin request is allowed.

طلب OPTIONS التلقائي للمتصفح للتحقق مما إذا كان طلب عبر الأصول مسموحاً.

Why It Matters

When 404Fault's frontend calls a Firebase Cloud Function from a different domain, the browser first sends an OPTIONS preflight.

عندما تستدعي واجهة 404Fault الأمامية Firebase Cloud Function من نطاق مختلف، يرسل المتصفح أولاً طلب OPTIONS تمهيدياً.

Full Definition

Before sending a cross-origin POST/PUT/DELETE request (or any request with custom headers), browsers automatically send an HTTP OPTIONS preflight request to check if the server allows it. The server must respond with CORS headers (Access-Control-Allow-Origin, Access-Control-Allow-Methods) or the browser blocks the actual request.
قبل إرسال طلب POST/PUT/DELETE عبر الأصول، ترسل المتصفحات تلقائياً طلب OPTIONS تمهيدياً للتحقق مما إذا كان الخادم يسمح به.

Example Usage

“When 404Fault's frontend calls a Firebase Cloud Function from a different domain, the browser first sends an OPTIONS preflight.”

“عندما تستدعي واجهة 404Fault الأمامية Firebase Cloud Function من نطاق مختلف، يرسل المتصفح أولاً طلب OPTIONS تمهيدياً.”

Knowledge Graph

AI Builder Tips

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Avoid these mistakes when using CORS Preflight:

1

Wondering why API calls work in curl/Postman but fail in the browser → Browsers enforce CORS; curl doesn't. Always test cross-origin requests from the actual browser.

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Help me build a project using CORS Preflight.

Explain:
1. What is CORS Preflight and why it matters
2. The core architecture and required tools
3. Step-by-step implementation plan
4. Common mistakes to avoid: Wondering why API calls work in curl/Postman but fail in the browser → Browsers enforce CORS; curl doesn't. Always test cross-origin requests from the actual browser.
5. Best practices and production tips

Official Resources

No official documentation link on file for CORS Preflight yet.

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