手写 instanceof

[MaMaFish]

instanceof 就是在实例的原型链中寻找构造函数的 Prototype

function myInstanceof(instance, constructer) {
    if (typeof instance !== 'object') {
        return false
    }
    while(true) {
        if (instance === null) {
            return false
        }
        if (instance.__proto__ === constructer.prototype) {
            return true
        }
        instance = instance.__proto__
    }
}

function Person (name) {
    this.name = name
}
const p1 = new Person('luo')
console.log(myInstanceof(p1, Person)) // true
console.log(myInstanceof(p1, Object)) // true