实现一个 instanceof

用来测试一个对象是否在其原型链中存在某个构造函数

function _instanceof(left, right) {
  var prototype = right.prototype;
  var proto = left.__proto__;
  while (true) {
    if (proto === null) return false;
    if (proto === prototype) return true;
    proto = proto.__proto__;
  }
}

ES6版本

function Instanceof(left: object, right: Function): boolean {
  let proto = Reflect.getPrototypeOf(left)
  const prototype = right.prototype
  
  while(true) {
    if (proto === null) return false;
    if (proto === prototype) return true;
   	proto = Reflect.getPrototypeOf(left)
  }
}