How to connect my backend with my frontend with angular2 and ionic2 using gridFs?

I have created a file in my database using gridFs.The is as follows:

storeAudio.js

var mongoose = require('mongoose');
var fs = require('fs');
var Grid = require('gridfs-stream');
Grid.mongo=mongoose.mongo;


//establish mongoDB connection
 mongoose.Promise = global.Promise;
var conn = mongoose.createConnection('mongodb://localhost:27017/aHolyBoly');
conn.once('open',function(){
   var gfs = Grid(conn.db);
 // var db = new mongo.Db('aHolyBoly', new mongo.Server("127.0.0.1", 27017));
//var gfs = Grid(db, mongo);

var writeStream = gfs.createWriteStream({
    filename:'song1.mp3'
});
fs.createReadStream('../list/hero.mp3').pipe(writeStream);
writeStream.on('close',function(file){
    console.log(file.filename +'Written to db');
});
});

Now I want to make an API using express and node so that I can connect my Backend with Frontend using Ionic2 and Angular2.So I saw this tutorial: https://www.joshmorony.com/building-a-review-app-with-ionic-2-mongodb-node/ Now in this tutorial, Http verbs get, post etc are used to make the api calls and then it is used as a provider.So is this the way to continue with my project?And if this is the way then I have some questions which are below:

In the link mentioned above there is server.js file.In that file a code as mongoose.connect('mongodb://localhost/reviewking'); Why this is used again if already used in my file storeAudio.js?

Secondly, The http verbs should be used in the similar fashion using gridFs?

Note:I am using first time everything (except ionic2 and angular2).Please let me know if any more inputs shoud be provided.And Sorry for the mistakes if found in this post.

via Aditya Jain