javascript对象属性的赋值解析

    function Animal(){}
   function Dog (age){
        this.name = 'fuck you' ;
        this.age = age
   }

   var dog = new Dog(12);
   console.log(dog); //{name: "fuck you", age: 12}
   Dog.prototype = Animal;
   var dog2 = new Dog(12);
   console.log(dog2);//{age: 12}

Object.getOwnPropertyNames(Animal) 
//["length", "name", "arguments", "caller", "prototype"]
//Animal有上述5个属性

Object.getOwnPropertyDescriptor(Animal, 'name')
//Object {value: "Animal", writable: false, enumerable: false, configurable: true}
//属性'name'只读，所以再次赋值无效

//通过知道属性只读，对象属性赋值操作无效，那么我们可以更改name的property-wirteable为true，如下
Object.defineProperty(Animal, 'name', {writable: true})
Object.getOwnPropertyDescriptor(Animal, 'name')
//Object {value: "Animal", writable: true, enumerable: false, configurable: true}

var dog3 = new Dog(13)
//Dog {name: "fuck you", age: 13}

//属性enumerable都为false，所以for in遍历不出来
Object.keys(Animal) //[]

//用ES6的Reflect
Reflect.ownKeys(Animal)
//["length", "name", "arguments", "caller", "prototype"]
Reflect.has(Animal,'name') //true