When I try to connect to mongodb in the command prompt it will display an error how to fix it?

events.js:160 throw er; // Unhandled 'error' event

  ^

MongoError: failed to connect to server [localhost:27017] on first connect [MongoError: connect ECONNREFUSED 127.0.0.1:27017]

at Pool.<anonymous> 

(C:\Users\DELL\Desktop\meanapp\server\node_modules\mongodb-

core\lib\topologies\server.js:328:35)

at emitOne (events.js:96:13)

at Pool.emit (events.js:188:7)

at Connection.<anonymous> 

(C:\Users\DELL\Desktop\meanapp\server\node_modules\mongodb-

core\lib\connection\pool.js:274:12)

via Erandi