My enumerable property is not enumerable

example.js

var Example = function() {

};

Object.defineProperty(Example.prototype,'message',{
  enumerable: true,
  set: function(v) {
    this._message = v;
  },
  get: function() {
    return this._message;
  }
});

var example = new Example();

example.message = "Test 123";
console.log(example);
console.log(example.propertyIsEnumerable('message'));
console.log(Object.keys(example));