Poller.js

const http = require('http');
const Firebase = require('firebase');

const FB_ROOT = new Firebase('https://scrapyard.firebaseio.com/');
const VK = {
  wallGet: {
  	// translating vk api to node http api
    reqOpts: function(opts) {
      return({
        host: 'api.vk.com',
        path: `/method/wall.get?domain=${opts.domain}&count=${opts.count}`
      });
    },

    // Selecting only new Posts
    getUpds:function(prevJson, newJson){
    	var prevPosts = prevJson ? JSON.parse(prevJson).response : null; // []
    	var newPosts = JSON.parse(newJson).response; // []

    	const prevCounter = prevPosts ? prevPosts.splice(0,1) : null; //remove first (counter)
    	const newCounter = newPosts.splice(0,1); //remove first (counter)

    	// pinned post is ignored
    	const prevDate = prevPosts ? ( prevPosts[0].is_pinned ? prevPosts[1].date : prevPosts[0].date ) : null; 
    	const newDate = newPosts[0].is_pinned ? newPosts[1].date : newPosts[0].date;

    	const updsArr = [];

    	updsArr.push(newCounter)

    	for (var i = 0, len = newPosts.length; i < len; i++) {
    		if ( newPosts[i].date > prevDate ) updsArr.push(newPosts[i]);
    	}

    	var updatedData = {
    		response: updsArr
    	}

    	if (!updatedData.response[1]) return null; // no actual data

    	return updatedData;

    },

    // What data to set in firebase
    jsonHandler: function(json){
      var fbObj = {};
      JSON.parse(json).response.forEach(function(post) {
        if (post.text) {
          fbObj[post.id] = {};
          fbObj[post.id].date = post.date;
          fbObj[post.id].text = post.text;
        }
      });
     
      return fbObj;
    }
  }
}


//---------------- Poller  -----------------

const vkPoller = function(vkMethod, vkMethodOpts, fbRef, interval) {
	const that = this;
	var prevJson = null; //for cheking updates;
	this.data = '';

	var canIterate = true;
	
	const iterator = setInterval(() => {
	  if (canIterate) {
	    var vkResJson = '';

	    (function(vkReq){

	     vkReq.on('response', (vkRes) => {
	       canIterate = false;

	       console.log(`VK Res Status: ${vkRes.statusCode}`);
	       console.log(`VK Res Headers: ${JSON.stringify(vkRes.headers)}`);

	       vkRes.setEncoding('utf8');

	       vkRes.on('data', (chunk) => {
	         vkResJson += chunk; // collecting data from chunks
	       });

	       vkRes.on('end', () => { // when all data is collected handling JSON for Fb and setting it

	        	var newData;
	        	if (vkResJson !== prevJson) {

	        		newData = VK[vkMethod].getUpds(prevJson, vkResJson);
	         		if (newData) fbRef.push(newData);

	        		prevJson = vkResJson; 
	        	}

	         //var fbJson = VK.wallGet.jsonHandler(vkResJSON);
	         
	         
	         that.data = newData; // for Web-Server
	         canIterate = true;
	       });

	     });

	     vkReq.on('error', (e) => {
	       console.log(`problem with request: ${e.message}`);
	     });

	     vkReq.end();

	   
	    })( http.request(VK[vkMethod].reqOpts(vkMethodOpts)) );

	  }

	}, interval);
}


//var puritymeth = new vkPoller('wallGet', {domain: 'puritymeth', count: 2}, FB_ROOT, 5 * 1000);
var pikabu = new vkPoller('wallGet', {domain: 'pikabu', count: 2}, FB_ROOT, 5 * 1000);

/*
setTimeout(function(){
  clearInterval(iterator);
  console.log('Polling aborted by timeout');
}, 20 * 1000);*/

//------------ Web-Server (for testing) ----------------

/*
const server = http.createServer();

server.on('request', function(req, res){
  res.writeHead(200, {
    'Content-type': 'text/json; charset=utf-8' // json, cyrillic
  });

  res.write(pikabu.data);
  res.end();
});

server.listen(80);

*/