An Observable object that emits change events

event-fun.js

const EventEmitter = require('events');                                                                                                                                               
                                                                                                                                                                                        
  class Observable extends EventEmitter {                                                                                                                                               
      constructor(source) {                                                                                                                                                             
          super();                                                                                                                                                                      
          this.self = {};                                                                                                                                                               
          for (let prop in source) {                                                                                                                                                    
              if (prop === 'self')                                                                                                                                                      
                  continue;                                                                                                                                                             
              this.self[prop] = source[prop];                                                                                                                                           
              Object.defineProperty(this, prop,.                                                                                                                                        
                  { set: function(value) {                                                                                                                                              
                      this.emit('change', { 'property': prop, 'old': this.self[prop], 'new': value });                                                                                  
                      this.self[prop] = value;                                                                                                                                          
                  }, get: function() {                                                                                                                                                  
                      return this.self[prop];                                                                                                                                           
                     }                                                                                                                                                                  
                  });                                                                                                                                                                   
          }                                                                                                                                                                             
      }                                                                                                                                                                                 
  }                                                                                                                                                                                     
                                                                                                                                                                                        
                                                                                                                                                                                        
  const bob = new Observable({ color: 'red', counter: 0, friends: [] });                                                                                                                
                                                                                                                                                                                        
  bob.on('change', (ev) => {                                                                                                                                                            
      console.log(`property ${ev.property} changed from ${ev.old} to ${ev.new}`);                                                                                                       
  });                                                                                                                                                                                   
                                                                                                                                                                                        
  const incr = setInterval( () => { bob.counter++; if (bob.counter > 10) { clearInterval(incr) } }, 150 );                                                                              
  setTimeout( () => { bob.color = 'blue' }, 100 );                                                                                                                                      
  setTimeout( () => { bob.color = 'green' }, 200 );                                                                                                                                     
  setTimeout( () => { bob.friends = [ ...bob.friends, 'Jerry' ] }, 100 );                                                                                                               
  setTimeout( () => { bob.friends = [ ...bob.friends, 'Donald' ] }, 100 );                                                                                                              
  setTimeout( () => { bob.friends = [ 'Todd', ...bob.friends ] }, 100 );                                                                                                                
  setTimeout( () => { bob.friends = [] }, 100 );                                                                                                                                        
  setTimeout( () => { bob.color = 'red' }, 100 );                                                                                                                                       
  setTimeout( () => { bob.color = 'blue' }, 100