Proxy.handler.get

var p = new Proxy(target, {
  get: function(target, property, receiver) {
  }
}

var p = new Proxy{}, {
  get: function(target, prop, receiver) {
    console.log('called: ' + prop
    return 10;
  }
}

console.log(p.a // "called: a"
                  // 10

var obj = {};
Object.defineProperty(obj, 'a', { 
  configurable: false, 
  enumerable: false, 
  value: 10, 
  writable: false 
}

var p = new Proxy(obj, {
  get: function(target, prop) {
    return 20;
  }
}

p.a; // TypeError is thrown