SOURCE

//递归实现instanceOf 
//其作用是检测fucntion.prototype是否存在于对象的原型链上
const instanceOfTest = (obj,fn)=>{
    //必须是具备原型的
    if(obj && !['object','function'].includes(typeof obj)){
     return false   
    } 

    //实例对象的原型
    const proto = Object.getPrototypeOf(obj)

    if(proto === fn.prototype){
        return true
    }else if(proto === null){
        return false
    }else{
        return instanceOfTest(proto,fn)
    }
}

function Cat(name){
    this.name = name
}
function Test(name){
    this.name = name
}
const dot = new Cat("blank")

console.log(instanceOfTest(dot,Test))