observe property by proxy

observe.js

     class Test extends EventTarget {
          constructor() {
              super();
              this.value = 0;
          }
     }

     const test = new Test();
     const t = new Proxy(test, {
         set: function(target, prop, value) {
              target[prop] = value;
              target.dispatchEvent(new Event(`${prop}_changed`));
              return true;
         },
         get: function(target, prop, receiver) {
             return Reflect.get(...arguments).bind(target);
         }
     });
     t.addEventListener('value_changed', () => {
         console.log('value changed');
     });

    t.value = 1;