UnhandledPromiseRejectionWarning: NodeJS pull request not working - node.js

Question

I am writting following request to unfollow a user. followers are added to the database as an array.
router.put("/:id/unfollow",async (req,res) => {
if(req.body.userId !== req.params.id){
try{
const user = await User.findById(req.params.id);
const currentUser = await User.findById(req.params.id);
if (user.followers.includes(req.body.userId)){
await user.updateOne({$pull:{followers:req.body.userId}});
await currentUser.updateOne({$pull:{followers:req.params.id}});
res.status(200).json("user has been unfollowed");
}else{
res.send(403).json("you already unfollowed this user ");
}
}catch (err){
res.status(500).json(err);
console.log("err");
}
} else{
res.status(403).json("You cant unfollow yourself")
}
})
When the request is sent via postamn with the correct userId postman says "forbidden"
and the terminal shows the following error.
Whats wrong in here ?
express deprecated res.send(status): Use res.sendStatus(status) instead routes\user.js:98:21
(node:15336) UnhandledPromiseRejectionWarning: Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
at ServerResponse.setHeader (_http_outgoing.js:561:11)
at ServerResponse.header (C:\Users\Banchi\Desktop\ReactTest\moodfix-api2\node_modules\express\lib\response.js:771:10)
at ServerResponse.send (C:\Users\Banchi\Desktop\ReactTest\moodfix-api2\node_modules\express\lib\response.js:170:12)
at ServerResponse.json (C:\Users\Banchi\Desktop\ReactTest\moodfix-api2\node_modules\express\lib\response.js:267:15)
at C:\Users\Banchi\Desktop\ReactTest\moodfix-api2\routes\user.js:102:29
at processTicksAndRejections (internal/process/task_queues.js:95:5)
(Use `node --trace-warnings ...` to show where the warning was created)
(node:15336) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a prom
ise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#c
li_unhandled_rejections_mode). (rejection id: 1)
(node:15336) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-z
ero exit code.

Answer 1

inside else block of try, make following change:
try{
...
if (user.followers.includes(req.body.userId)){
...
res.status(200).json("user has been unfollowed");
} else{
// res.send(403).json("you already unfollowed this user ");
// ^^^ here is the error. It should be
res.status(403).json("you already unfollowed this user ");
}
} catch ...
Cannot set headers after they are sent to the client
This happens when you send another response behind an already sent one. And your code is doing this. First it respond with send(403) then sending json("you already unfollowed this user ") as well.