获取JSON中的对象总数，但Javascript Object.keys().length返回未定义

function getObjectCount(json) {
  let count = 0;
  for (let key in json) {
    if (json.hasOwnProperty(key)) {
      count++;
    }
  }
  return count;
}

const json = {
  "key1": "value1",
  "key2": "value2",
  "key3": "value3"
};

const count = getObjectCount(json);
console.log(count); // 输出：3

const json = {
  "key1": "value1",
  "key2": "value2",
  "key3": "value3"
};

const keys = Object.keys(json);
const count = keys.length;
console.log(count); // 输出：3