手写new操作符(完整版包含格式检验)

function Dog(name) {
    this.name = name;
}
Dog.prototype.bark = function () {
    console.log('wangwang');
};
Dog.prototype.sayName = function () {
    console.log('my name is ' + this.name);
};

/* let sanmao = new Dog('三毛');
sanmao.sayName();
sanmao.bark(); */

// Ctor:构造函数  params:给构造函数传递的实参(数组)
//   + Object.create([prototype]) 创建一个空对象，并且让其__proto__指向[prototype]
//   + Object.create(null) 创建一个不具备原型链的空对象
/* function _new(Ctor, ...params) {
    // 格式校验：函数 & 有原型对象 & 不是Symbol/BigInt
    if (typeof Ctor !== "function") throw new TypeError(`${Ctor} is not a constructor!`);
    let name = Ctor.name,
        proto = Ctor.prototype;
    if (/^(Symbol|BigInt)$/i.test(name) || !proto) throw new TypeError(`${name} is not a constructor!`);

    // 1.创建当前类的一个实例对象
    /!* let obj = {};
    obj.__proto__ = Ctor.prototype; *!/
    let obj = Object.create(Ctor.prototype);

    // 2.把构造函数像普通函数一样执行，但是this需要指向创建的实例对象
    let result = Ctor.call(obj, ...params);

    // 3.看函数的返回值，如果没有写返回值，或者返回的是原始值，我们默认返回实例对象；如果返回的是对象，则以自己返回的为主；
    if (result !== null && /^(object|function)$/i.test(typeof result)) return result;
    return obj;
} */

const _new = function _new(Ctor, ...params) {
    if (typeof Ctor !== "function") throw new TypeError(`${Ctor} is not a constructor!`);
    let name = Ctor.name,
        proto = Ctor.prototype,
        obj,
        result;
    if (/^(Symbol|BigInt)$/i.test(name) || !proto) throw new TypeError(`${name} is not a constructor!`);
    obj = Object.create(proto);
    result = Ctor.call(obj, ...params);
    if (result !== null && /^(object|function)$/i.test(typeof result)) return result;
    return obj;
};
let sanmao = _new(Dog, '三毛');
sanmao.bark(); //=>"wangwang"
sanmao.sayName(); //=>"my name is 三毛"
console.log(sanmao instanceof Dog); //=>true

标签：function,obj,name,result,new,手写,完整版,Ctor
来源： https://blog.csdn.net/Donnien/article/details/118093354