i am encounting the error while running server.js

[sanketbisne]

Microsoft Windows [Version 10.0.17134.829]
(c) 2018 Microsoft Corporation. All rights reserved.

C:\Users\HP\Desktop\modified Sknchat>npm start

modified-sknchat@1.0.0 start C:\Users\HP\Desktop\modified Sknchat
node server.js

(node:18280) DeprecationWarning: current URL string parser is deprecated, and will be removed in a future version. To use the new parser, pass option { useNewUrlParser: true } to MongoClient.connect.
(node:18280) DeprecationWarning: current Server Discovery and Monitoring engine is deprecated, and will be removed in a future version. To use the new Server Discover and Monitoring engine, pass option { useUnifiedTopology: true } to the MongoClient constructor.
C:\Users\HP\Desktop\modified Sknchat\node_modules\mongodb\lib\topologies\server.js:240
throw err;
^

MongoNetworkError: failed to connect to server [127.0.0.1:27017] on first connect [MongoNetworkError: connect ECONNREFUSED 127.0.0.1:27017]
at Pool. (C:\Users\HP\Desktop\modified Sknchat\node_modules\mongodb\lib\core\topologies\server.js:431:11)
at Pool.emit (events.js:182:13)
at connect (C:\Users\HP\Desktop\modified Sknchat\node_modules\mongodb\lib\core\connection\pool.js:580:14)
at makeConnection (C:\Users\HP\Desktop\modified Sknchat\node_modules\mongodb\lib\core\connection\connect.js:39:11)
at callback (C:\Users\HP\Desktop\modified Sknchat\node_modules\mongodb\lib\core\connection\connect.js:261:5)
at Socket.err (C:\Users\HP\Desktop\modified Sknchat\node_modules\mongodb\lib\core\connection\connect.js:286:7)
at Object.onceWrapper (events.js:273:13)
at Socket.emit (events.js:182:13)
at emitErrorNT (internal/streams/destroy.js:82:8)
at emitErrorAndCloseNT (internal/streams/destroy.js:50:3)
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! modified-sknchat@1.0.0 start: node server.js
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the modified-sknchat@1.0.0 start script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR! C:\Users\HP\AppData\Roaming\npm-cache_logs\2019-09-17T18_05_33_397Z-debug.log

C:\Users\HP\Desktop\modified Sknchat>