new 创建对象发生了什么

参考自：new创建对象的过程发生了什么

示例代码：

function Person(name) {
    this.name = name;
}
Person.hairColor = "black";
Person.prototype.say = function() {
    console.log("My name is " + this.name);
};
var john = new Person("John");
console.log(
    john.name, // "John",
    john.hairColor, // undefined
    john.height // undefined
);
john.say(); // "My name is John"
console.log(
    Person.name, // "Person"
    Person.hairColor // "black"
);
Person.say(); // Person.say is not a function

解析：

var john = new Person("John") = {
    var obj = {};
    obj.__proto__ = Person.prototype; // 此时便建立了obj对象的原型链：
    // obj->Person.prototype->Object.prototype->null
    var result = Person.call(obj,"John"); // 相当于obj.Person("John")
    return typeof result === 'object' ? result : obj; // 如果无返回值或者返回一个非对象值，则将obj返回作为新对象
}