如何检查JavaScript对象是否直接是`{}`实例,而不是子类？

function isObjectInstance(obj) {
  return Object.getPrototypeOf(obj) === null;
}

function isSubclassObject(obj) {
  return Object.getPrototypeOf(obj) !== null;
}

function testObject() {
  const obj1 = {};
  const obj2 = new Object();
  const obj3 = new Object();
  const obj4 = {};

  console.log(isObjectInstance(obj1)); // true
  console.log(isObjectInstance(obj2)); // false
  console.log(isObjectInstance(obj3)); // true
  console.log(isObjectInstance(obj4)); // true

  console.log(isSubclassObject(obj1)); // false
  console.log(isSubclassObject(obj2)); // true
  console.log(isSubclassObject(obj3)); // false
  console.log(isSubclassObject(obj4)); // false
}

testObject();