手写instanceof

手写instanceof

function myInstance(obj1, obj2) {
    let obj1Proto = obj1.__proto__;
    while(true) {
        // null.__proto__为空
        if (obj1Proto == null) {
            return false;
        }
        if (obj1Proto == obj2.prototype) {
            return true;
        }
        obj1Proto = obj1Proto.__proto__;
    }    
}

class Person{
    constructor(name, age) {
        this.name = name;
        this.age = age;
    }
}
// 子类继承
class Student extends Person {
    constructor(name, age, sex) {
        super(name, age);
        this.sex = sex;
    }
}
function myInstance(obj1, obj2) {
    let obj1Proto = obj1.__proto__;
    while(true) {
        // null.__proto__为空
        if (obj1Proto == null) {
            return false;
        }
        if (obj1Proto == obj2.prototype) {
            return true;
        }
        obj1Proto = obj1Proto.__proto__;
    }    
}
// 实例化
const zhangsan = new Student("张三",18,"男");
console.log(myInstance(zhangsan, Student)); // true
console.log(myInstance(zhangsan, Person)); // true
console.log(myInstance(zhangsan, Object)); // true
console.log(myInstance(zhangsan, Array)); // false