编辑代码

function myNew(fn, ...args) {
    //创建一个空对象
    let obj = Object.create(null);
    //obj.prototype==fun.__proto__ 
    //将空对象的原型，指向构造函数的原型
    Object.setPrototypeOf(obj, fn.prototype)
    //改变this指向，将this指向空对象
    let result = fn.apply(obj, args)
    //判断该函数的是否有返回
    return result ? result : obj;
}
function Test(age, name) {
    this.age = age;
    this.name = name;
}

const myTest = myNew(Test, 18, '张三');
console.log(myTest.name)
console.log(myTest.__proto__ === Test.prototype);
console.log(myTest instanceof Test);

function test2() {
    return 2
}
const myTest2 = myNew(test2)
console.log(myTest2)