I've tried connecting my mongoose to my express app, using the following, it'd then connect at first and then state error later on

Code:

mongoose.connect('mongodb://localhost:27017/blog'), {
    useUnifiedTopology: true,
    useNewUrlParser: true,
  }

console.log('MongoDB connected successfully!!');

output:

MongoDB connected successfully!!
(node:2868) UnhandledPromiseRejectionWarning: MongooseServerSelectionError: connect ECONNREFUSED 127.0.0.1:27017
    at NativeConnection.Connection.openUri (C:\Users\v\Desktop\News Blog\node_modules\mongoose\lib\connection.js:824:32)
    at C:\Users\v\Desktop\News Blog\node_modules\mongoose\lib\index.js:381:10
    at C:\Users\v\Desktop\News Blog\node_modules\mongoose\lib\helpers\promiseOrCallback.js:41:5
    at new Promise (<anonymous>)
    at promiseOrCallback (C:\Users\v\Desktop\News Blog\node_modules\mongoose\lib\helpers\promiseOrCallback.js:40:10)
    at Mongoose._promiseOrCallback (C:\Users\v\Desktop\News Blog\node_modules\mongoose\lib\index.js:1234:10)
    at Mongoose.connect (C:\Users\v\Desktop\News Blog\node_modules\mongoose\lib\index.js:380:20)
    at Object.<anonymous> (C:\Users\v\Desktop\News Blog\server.js:7:10)
    at Module._compile (internal/modules/cjs/loader.js:1068:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1097:10)
(Use `node --trace-warnings ...` to show where the warning was created)
(node:2868) 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(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1)
(node:2868) [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.