AJAX数据中嵌套JSON字符串的解析与处理：避免属性访问undefined

{
  "name":"SOUMITRA AND & SARKAR",
  "address":"24/1 Sahid Ananta Dutta Sarani, P.O. Rajbari,Kolkata 700 081",
  "stateid":["19","20","21"],
  "ref":{"noref":01,"myref":"02"}
}

[
  {
    "maindata":"{
        \"name\":\"SOUMITRA AND & SARKAR\",
        \"address\":\"24/1 Sahid Ananta Dutta Sarani, P.O.Rajbari, Kolkata 700 081\",
        \"stateid\":[\"19\",\"20\",\"21\"],
        \"ref\":{\"noref\":01,\"myref\":\"02\"}
     }"
   }
]

const pass_data = [
  {
    "maindata":"{
        \"name\":\"SOUMITRA AND & SARKAR\",
        \"address\":\"24/1 Sahid Ananta Dutta Sarani, P.O.Rajbari, Kolkata 700 081\",
        \"stateid\":[\"19\",\"20\",\"21\"],
        \"ref\":{\"noref\":01,\"myref\":\"02\"}
     }"
   }
];

for (let i = 0; i < pass_data.length; i++) {
    // pass_data[i].maindata 会显示整个 JSON 字符串，例如：
    // "{ \"name\":\"SOUMITRA AND & SARKAR\", ... }"
    console.log("原始 maindata:", pass_data[i].maindata);

    // 尝试直接访问其内部属性，结果是 undefined
    console.log("尝试访问 address:", pass_data[i].maindata.address); // 输出: undefined
    console.log("尝试访问 name:", pass_data[i].maindata.name);     // 输出: undefined
}

const ajaxResult = [
  {
    "maindata":"{
        \"name\":\"SOUMITRA AND & SARKAR\",
        \"address\":\"24/1 Sahid Ananta Dutta Sarani, P.O.Rajbari, Kolkata 700 081\",
        \"stateid\":[\"19\",\"20\",\"21\"],
        \"ref\":{\"noref\":01,\"myref\":\"02\"}
     }"
   }
];

// 遍历数据，对每个对象的 maindata 字段进行二次解析
for (let i = 0; i < ajaxResult.length; i++) {
    // 将 maindata 字符串解析为 JavaScript 对象
    ajaxResult[i].maindata = JSON.parse(ajaxResult[i].maindata);
}

// 现在可以正确访问内部属性了
console.log("解析后的 address:", ajaxResult[0].maindata.address); // 输出: "24/1 Sahid Ananta Dutta Sarani, P.O.Rajbari, Kolkata 700 081"
console.log("解析后的 name:", ajaxResult[0].maindata.name);     // 输出: "SOUMITRA AND & SARKAR"

// 模拟AJAX返回的原始数据
const rawAjaxData = [
  {
    "id": 1,
    "timestamp": "2023-10-27T10:00:00Z",
    "maindata":"{
        \"name\":\"SOUMITRA AND & SARKAR\",
        \"address\":\"24/1 Sahid Ananta Dutta Sarani, P.O.Rajbari, Kolkata 700 081\",
        \"stateid\":[\"19\",\"20\",\"21\"],
        \"ref\":{\"noref\":1,\"myref\":\"02\"}
     }"
   },
   {
    "id": 2,
    "timestamp": "2023-10-27T10:05:00Z",
    "maindata":"{
        \"name\":\"JOHN DOE\",
        \"address\":\"123 Main St, Anytown, USA\",
        \"stateid\":[\"01\",\"02\"],
        \"ref\":{\"noref\":2,\"myref\":\"03\"}
     }"
   },
   {
    "id": 3,
    "timestamp": "2023-10-27T10:10:00Z",
    "maindata":"invalid json string" // 模拟一个无效的JSON字符串
   }
];

// 处理数据
const processedData = rawAjaxData.map(item => {
    // 确保 maindata 存在且为字符串类型
    if (typeof item.maindata === 'string') {
        try {
            // 尝试解析 maindata 字符串
            item.maindata = JSON.parse(item.maindata);
        } catch (e) {
            // 如果解析失败，打印错误并可以将 maindata 设置为 null 或空对象
            console.error(`解析 maindata 失败 (ID: ${item.id}):`, e);
            item.maindata = null; // 或者 {}
        }
    }
    return item;
});

console.log("\n--- 处理后的数据 ---");
processedData.forEach(item => {
    if (item.maindata) {
        console.log(`ID: ${item.id}, Name: ${item.maindata.name}, Address: ${item.maindata.address}`);
    } else {
        console.log(`ID: ${item.id}, maindata 无效或已清除`);
    }
});

// 验证特定项
console.log("\n--- 验证特定项 ---");
console.log("第一项的地址:", processedData[0].maindata.address);
console.log("第二项的引用:", processedData[1].maindata.ref.myref);
console.log("第三项的 maindata (应为 null):", processedData[2].maindata);