将对象转换为字符串并在值不存在的情况下填充NA

function convertObjectToStringWithNA(obj) {
  if (obj && typeof obj === "object") {
    // 遍历对象的属性
    for (let key in obj) {
      if (obj.hasOwnProperty(key)) {
        // 判断属性值是否为null或undefined
        if (obj[key] === null || obj[key] === undefined) {
          obj[key] = "NA";
        } else {
          obj[key] = obj[key].toString();
        }
      }
    }
  }
  
  // 将对象转换为字符串并返回
  return JSON.stringify(obj);
}

// 示例使用
let exampleObj = {
  name: "John",
  age: 30,
  occupation: null,
  hobby: undefined
};

console.log(convertObjectToStringWithNA(exampleObj));