更改构造函数属性后，对象仍然是原始构造函数的实例

Question

我很困惑为什么在将对象的构造函数属性更改为指向另一个函数之后，该对象仍然是旧构造函数的实例

//Original Constructor
      function orig_cons() {}

//New Constructor
  function new_cons(){}

 //Adding property to myfun prototype
  new_cons.prototype.x = 1;

 //Invoking a new object of 1st constructor
  var obj1 = new orig_cons();

//check obj1 instanceof 1st constructor
 console.log(obj1 instanceof orig_cons); // true

 //Changing constructor property to point to 2nd function
  obj1.constructor = new_cons;

//check obj1 instanceof 2nd function
 console.log(obj1 instanceof new_cons); // false

而且obj1的prototype属性还是原来构造函数的prototype：

       console.log(Object.getPrototypeOf(obj1)); //orig_cons {}

Answer 1

instanceof 检查对象的原型而不是构造函数，举个例子：

function Person(name){
  this.name = name;
}

var  p = new Person();

console.log(p instanceof Person); //true

function Func(){}

p.constructor = Func;

console.log(p instanceof Person); // true

Person.prototype = {};

console.log(p instanceof Person); // false

注意更改原型如何影响instanceof。

来自 MDN：https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/instanceof

instanceof 操作符测试constructor.prototype 在 对象的原型链。