JavaScript面向对象编程实现模拟

function Person(name ){
  this.name = name;
};
const jack = new Person('jack'); //Person {name: 'jack'}
function Person(name ){
  this.name = name;
  return name;
};
const jack = new Person('jack'); //Person {name: 'jack'}
function Person(name ){
  this.name = name;
  return ['jack'];
};
const jack = new Person('jack'); //['jack']

function Person(name ){
  this.name = name;
};
const jack = new Person('jack');
const tom = new Person('tom');
console.log(jack); //Person {name: 'jack'}
console.log(tom); //Person {name: 'tom'}

function Person(){
  this.name = name;
};
const jack = Person('jack'); //undefined

function Person(name){
 if(!(this instanceof Person)){
  return new Person(name);
 };
 this.name = name;
};

Person(name); //Object { name: "jack" }

function Person(){
  console.log(new.target);
};
new Person(); //function Person(){...}
Person(); //undefined

    function Person(name){
      if(!(new.target === Person)){
           return new Person(name);
      };
      this.name = name;
    };
    console.log(Person('jack')); //Object { name: "jack" }

  function myNew() {
      const args = Array.prototype.slice.call(arguments);
      const construct = args.shift();
      //创建this,并将原型设置为构造函数的prototype
      const context = Object.create(construct.prototype);
      //执行构造函数,注意这里参数是数组形式所以使用apply
      construct.apply(context, args);
      //返回
      const res = construct();
      if ((typeof res === 'object' || res === 'function') && typeof res !== 'null') {
        return res;
      } {
        return context;
      }
    };
    function Person(name, age) {
      this.name = name;
      this.age = age;
    };
    const jack = myNew(Person, 'jack', 21);
    //Person {name: 'jack', age: 21}