instanceof

instanceof 运算符用于检测构造函数的 prototype 属性是否出现在某个实例对象的原型链上。

语法

object instanceof constructor;

参数

• object: 某个实例对象
• constructor: 某个构造函数

示例

function Car(make, model, year) {
  this.make = make;
  this.model = model;
  this.year = year;
}
const auto = new Car('Honda', 'Accord', 1998);

console.log(auto instanceof Car); // true
console.log(auto instanceof Object); // true

手写实现

function instabceof(target, origin) {
  while (target) {
    if (Object.getPrototypeOf(target) === origin.prototype) return true;
    target = Object.getPrototypeOf(target);
  }
  return false;
}

console.log(instabceof(auto, Car)); // true
console.log(instabceof(auto, Object)); // true