js返回值 undefined

function calculateSum(a, b) {
    return a + b; // 明确返回计算结果
}

let config = {
    timeout: 5000,
    retries: undefined // 使用默认值初始化
};

// 检查属性是否存在
if (config.retries !== undefined) {
    // 执行相关操作
}

function fetchData(url) {
    let data;
    try {
        data = fetch(url).then(response => response.json());
    } catch (error) {
        console.error('Fetch error:', error);
    }
    return data;
}

let result = fetchData('https://api.example.com/data');
if (result === undefined) {
    console.log('Failed to fetch data.');
} else {
    console.log('Data fetched successfully:', result);
}