instanceof 就是判断构造函数的 prototype 属性是否出现在实例的原型链上。
function instanceOf(left, right) {
let proto = left.__proto__
let prototype = right.prototype
while (true) {
if (proto === null) return false
if (proto === prototype) return true
proto = proto.__proto__
}
}
console.log(instanceOf(() => {}, Function))