在这种情况下如何创建对象？

Question

在这种情况下 prototype 对象不再有 constructor 属性。这里只是一个空对象。但是，尽管如此，new obj.constructor 仍然以某种方式创建了一个空对象。怎么样？

function Constructor() { 
    this.name = 'Kira';
    this.age = 35;
    this.city = 'New-York';
}; 
Constructor.prototype = {};

let obj = new Constructor;
let obj2 = new obj.constructor;
console.log(obj2); //{}

这里也创建了对象。在 Chrome 浏览器的控制台中，它显示为 String.

function User(name) {
  this.name = name;
}
User.prototype = {};

let user = new User('John');
let user2 = new user.constructor('Pete');

console.log(user2);

怎么可能？这里的对象是如何创建的？

Answer 1

将原型设置为 {} 并不意味着没有属性。这意味着唯一的属性是您会在新对象上找到的属性。特别是，constructor 属性来自原型并指向 Object

const o = {};

console.log("has constructor property:",
  "constructor" in o);
console.log("constructor property is own:", 
  o.hasOwnProperty("constructor"));
console.log("constructor property comes from prototype:",
  Object.getPrototypeOf(o).hasOwnProperty("constructor"));
console.log("constructor property is Object():",
  o.constructor === Object);

因此，当您调用 new obj.constructor 时，它等同于 new Object。

function Foo() {}; 
Foo.prototype = {};

let obj = new Foo;
console.log(obj.constructor === Object);
console.log(obj.constructor === ({}).constructor);
let obj2 = new obj.constructor;
console.log(obj2); //{}

当调用 new user.constructor('Pete'); 时，它再次只是调用全局 Object，因此它与 new Object('Pete') 相同。如果您传递一个具有对象包装器的值，您将从构造函数中获取该包装器：

const pete = new Object('Pete');
console.log(typeof pete, pete instanceof String);

const answer = new Object(42);
console.log(typeof answer, answer instanceof Number);

在这种情况下如何创建对象？

How come the object is created in this case?

javascript

prototype

object