SOURCE

function Person(name,age){
    this.name = name;
    this.age = age;
}
Person.prototype.sayName = function(){
    alert(this.name);
}

function myNew(func, ...args) {
    const obj ={};
    obj.__proto__ = func.prototype;
    let result = func.apply(obj,args);
    return result instanceof Object ? result : obj;
}


const lucy = myNew(Person,'lucy',23);
console.log(lucy);
lucy.sayName();