<------------------------{asyncHandler}------------------------>

const registerUser = asyncHandler(async (req, res) => {

const { name, email, password } = req.body;

// throw error or await something here

});

const registerUser = async (req, res, next) => {

try {

const { name, email, password } = req.body;

} catch (err) {

next(err);

}

};

How Express Handles Errors

When an error is passed to next(error), Express looks for an error-handling middleware like this:

app.use((err, req, res, next) => { res.status(500).json({ message: err.message }); });

So if something like await User.create() fails inside your registerUser function, it will be caught and handled gracefully.

------------------------------------------------------------------------ if ( req.headers.authorization && req.headers.authorization.startsWith('Bearer') ) This is a conditional check to see if the incoming HTTP request has a valid authorization header that looks like a Bearer token.

✅ req.headers.authorization This checks if the request has an Authorization header.

Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6... If the header is missing, this part will be undefined, and the condition fails.

✅ .startsWith('Bearer') This ensures that the value of authorization starts with the word "Bearer".

JWT tokens are commonly sent like this: Bearer So this checks whether the header follows the expected format.

--------------------------------<>---------------------------------------------------

---------------------------------------------------------------------

const users = await User.find(keyword).find({ _id: { $ne: req.user._id } }).select("-password");

✅ .find({ _id: { $ne: req.user._id } }) Adds an additional filter: exclude the current user from the results.

$ne means “not equal” in MongoDB.

req.user._id refers to the ID of the currently logged-in user.

So this ensures the user doesn't see themselves in the search results.

✅ .select("-password") Tells Mongoose to exclude the password field from the results.

"-password" means “do not include this field”.

Important for security reasons — you don’t want to expose user passwords (even if hashed).

<<........................................>>

Expression	Sends to...	Includes Sender?
io.emit(event, data)	Everyone connected	✅ Yes
socket.emit(event, data)	Only sender	✅ Yes
socket.broadcast.emit(event, data)	Everyone except sender	❌ No
socket.in(room).emit(event, data)	Everyone in room except sender	❌ No
io.in(room).emit(event, data)	Everyone in room (including sender)	✅ Yes