Real time refreshing app using Angular2

Question

I created a nodejs backend to get the current exchange rate from an API and display it in the html. Also I created the currency exchange component and its working fine. What I need to update the html and the currency exchange component every 5 or 10 seconds.

My first question is if its better to do it in the backend or the frontend, and the second is how I do it.

Here is my code:

api.js

const express = require('express');
const router = express.Router();

// declare axios for making http requests
const axios = require('axios');
const coinTicker = require('coin-ticker');

/* GET api listing. */
router.get('/', (req, res, next) => {
  res.send('api works');
});

router.get('/posts', function(req, res, next) {
  coinTicker('bitfinex', 'BTC_USD')
    .then(posts => {
      res.status(200).json(posts.bid);
    })
    .catch(error => {
      res.status(500).send(error);
    });
});



module.exports = router;

prices.component

import { Component, OnInit } from '@angular/core';
import { PricesService } from '../prices.service';
import { Observable } from 'rxjs';

@Component({
  selector: 'app-posts',
})
export class PricesComponent implements OnInit {
  // instantiate posts to an empty array
  prices: any;

  targetAmount = 1;
  baseAmount = this.prices;

  update(baseAmount) {
    this.targetAmount = parseFloat(baseAmount) / this.prices;
  }

  constructor(private pricesService: PricesService) { }

  ngOnInit() {
    // Retrieve posts from the API
    this.pricesService.getPrices().subscribe(prices => {
      this.prices = prices;
      console.log(prices);
    });
  }

}

Prices.service

import { Injectable } from '@angular/core';
import { Http } from '@angular/http';
import 'rxjs/add/operator/map';

@Injectable()
export class PricesService {

  constructor(private http: Http) { }

  // Get all posts from the API
  getPrices() {
    return this.http.get('/api/posts')
      .map(res => res.json());
  }
}

html

<div class="form-group">
     <label for="street">Tipo de Cambio</label>
     <input type="number" class="form-control" id="street" [value]="prices" disabled> CLP = 1 BTC
 </div>

Answer 1

You can use client side normal polling. It's very easy to implement client side polling using rxjs.

Try this:

return Observable.interval(5000) // call once 5 per second
    .startWith(0)
    .switchMap(() => {
        return this.http.get('/api/posts')
            .map(res => res.json())
    })
    .map(value => value[0]);