Fix: Add type validation for sendStatus to prevent BigInt serialization error (#6756)

[Vedant224]

Fixes #6756

This PR adds type validation to res.sendStatus() to prevent uncaught TypeError when BigInt values are passed as status codes.

Problem:

• res.sendStatus(200n) caused uncaught "Do not know how to serialize a BigInt" error
• Error occurred when sendStatus() called this.status() which internally uses JSON.stringify()

Solution:

• Add type checking at the beginning of sendStatus() method
• Throw consistent TypeError: Invalid status code for non-number inputs
• Matches existing error handling patterns in Express

Changes:

• Add type validation in lib/response.js
• Add test case for BigInt input in test/res.sendStatus.js
• All existing tests pass (1239 passing)
• Follows existing error message format
• No linting errors

Testing:

npm test  # All 1239 tests pass
npm run lint  # No errors

[shivarm]

Suggested change

	throw new TypeError('Invalid status code: ' + statusCode);
	throw new TypeError(`statusCode must be a valid number to res.sendStatus`);

I think it seems consistent

[bjohansebas]

agree

[bjohansebas]

This looks good, although this will be released for version 6 since it would be a breaking change, and we should first release a warning in version 5. Could you create a new PR to add a deprecation message?

[Vedant224]

@bjohansebas I've created the deprecation warning PR as requested. I kept it targeting master since that shows my actual 2-file changes cleanly. When I tried changing the target to 5.x it showed 36 changes (difference between branches).

Should I leave it targeting master and you'll handle getting it into Express v5, or would you prefer a different approach for the branch targeting?

The deprecation warning PR is ready for review - it adds the deprecate() call for non-number values in sendStatus().