Node basic examples

events.js

// DOCS https://nodejs.org/api/events.html
const Emitter = require('events');

class Basket extends Emitter {
  constructor(total) {
    super();
    this.total = total || 0;
    this.currency = '£';
  }
  
  init() {
    this.initialised = true;
    this.items = [];
    this.emit('onInit', this.currency);
  }
  
  add({amount, price, productId}) {
    this.items = [...this.items, 
      {
        amount,
        price,
        productId,
      }];
    this.emit('added', productId);
  }
}
const basket = new Basket(200);

basket.once('onInit', function(currency) {
  console.log(`New Basket created with value ${this.total}${currency}`);
});

basket.init(); // fires listener
basket.init(); // no log
basket.init(); // no log
basket.init(); // no log
basket.init(); // no log

basket.on('added', function(pid) {
  console.log(`Added ${pid}`);
});

// logs every time
basket.add({productId: 0});
basket.add({productId: 10});
basket.add({productId: 20});
basket.add({productId: 30});

// Always remove the listeners when they are not needed anymore
basket.removeAllListeners('added');
basket.removeAllListeners('onInit');