MongoError: failed to connect to server [localhost:27017]

This is my db.js:

import mongoose from 'mongoose';
export default () => {
 mongoose.Promise = global.Promise;
 mongoose.connect('mongodb://localhost/meetupapp');
 mongoose.connection
     .once('open', () => console.log('Mongodb running'))
    .on('error', err => console.error(err));
};

and this is the error message: MongoError: failed to connect to server [localhost:27017] on first connect] name: 'MongoError

I've installed mongodb!

via Denis Doan