七、instanceOf

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))