(node:3966) UnhandledPromiseRejectionWarning: Error: querySrv ECONNREFUSED - node.js

Question

I'm trying to fix an error UnhandledPromiseRejectionWarning: Error: querySrv ECONNREFUSED when I make an axios call to fetch user data from mongoose query without internet connection. I've tried to wrap both the mongoose query User.findOne() and mongoose.connect() with try catch, but the error still remain.
(node:3966) UnhandledPromiseRejectionWarning: Error: querySrv
ECONNREFUSED _mongodb._tcp.cluster1-94jth.mongodb.net [0] at
QueryReqWrap.onresolve [as oncomplete] (dns.js:196:19) [0] (node:3966)
UnhandledPromiseRejectionWarning: Unhandled promise rejection. This
error originated either by throwing inside of an async function
without a catch block, or by rejecting a promise which was not handled
with .catch(). (rejection id: 1) [0] (node:3966) [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-zero exit code.
FRONT-END
client.js
try {
const res = await axios.get('/auth/user?', {
params: {
refreshToken: refreshToken,
userID: userID
}
}
);
console.log(res.data);
} catch (error) {
if(error.toJSON().message === 'Network Error'){
alert('no internet connection');
}
}
BACK-END
auth.routes.js
auth.get(
'/user',
async(req, res)=>{
try {
const {userID, refreshToken, uniqueDeviceID, authTimestamp} = req.query;
const existingUser = await User.findOne({
$and: [
{'user_id': userID},
{'refresh_token': refreshToken}
]
});
res.send(existingUser);
} catch (error) {
console.log(error);
}
}
);
server.js
try {
mongoose.connect(keys.mongoURI, {useNewUrlParser: true, useUnifiedTopology: true, useCreateIndex: true});
console.log('Database Connected');
} catch (error) {
console.log(error);
}

Answer 1

Wrapping mongoose.connect with try/catch will not work because its no doing async/await.
You should:
mongoose.connect(keys.mongoURI, {useNewUrlParser: true, useUnifiedTopology: true, useCreateIndex: true})
.then(() => console.log('Database Connected'))
.catch(error=> console.log(error));

Answer 2

try/catch won't work with an asynchronous function without await
so to catch an error from asynchronous function:
try {
await someAsyncFunction();
} catch (e) {
//...
}
or you could use catch method from Promise or even use callbacks.