JavaScript new对象的四个过程

Posted 2022-01-04 xiaosongjiang

new 一个对象

function Person(name, age)   
	this.name = name;  
	this.age = age;   
  
var person = new Person("hellen", 23);

 

1、创建一个空对象

var obj = new Object(); 

2、让Person中的this指向obj，并执行Person的函数体

var result = Person.apply(obj,arguments);  

3、设置原型链，将obj的__proto__成员指向了Person函数对象的prototype成员对象

obj.__proto__ = Person.prototype; 

4、判断Person的返回值类型，如果是值类型，返回obj。如果是引用类型，就返回这个引用类型的对象。

if (typeof(result) == "object") 
	person = result;  
else
	person = obj;

 

function Person (name, age) 
  this.name = name;
  this.age = age;

Person.prototype.sayName = function () 
  console.log(this.name);
;
var person = new Person(‘Hellen‘, 23);
person.sayName();
console.log(person instanceof Person);

function New () 
  let obj = new Object();
  let fn = [].shift.call(arguments);
  let args = arguments;
  var ret = fn.apply(obj, args);
  obj.__proto__ = fn.prototype;
  return typeof ret === ‘object‘ ? ret : obj;

let person1 = New(Person, ‘Bob‘, 23);
person1.sayName();
console.log(person1 instanceof Person);