异步 HTTP 请求

fetch 是一个用于进行异步 HTTP 请求的 JavaScript API。

`fetch` 基本用法

// 使用 fetch 进行 GET 请求
fetch('https://api.example.com/data')
    .then(response => {
        // 检查响应是否成功
        if (!response.ok) {
            throw new Error('Network response was not ok');
        }
        // 解析响应数据为 JSON
        return response.json();
    })
    .then(data => {
        // 处理 JSON 数据
        console.log(data);
    })
    .catch(error => {
        // 处理错误
        console.error('There has been a problem with your fetch operation:', error);
    });

发送 POST 请求

// 使用 fetch 进行 POST 请求
fetch('https://api.example.com/data', {
    method: 'POST', // 指定请求方法为 POST
    headers: {
        'Content-Type': 'application/json' // 设置请求头
    },
    body: JSON.stringify({
        key1: 'value1',
        key2: 'value2'
    }) // 将数据转换为 JSON 字符串
})
    .then(response => {
        if (!response.ok) {
            throw new Error('Network response was not ok');
        }
        return response.json();
    })
    .then(data => {
        console.log(data);
    })
    .catch(error => {
        console.error('There has been a problem with your fetch operation:', error);
    });

处理不同的响应格式

fetch('https://api.example.com/data')
    .then(response => {
        // 处理文本响应
        return response.text();
    })
    .then(text => {
        console.log(text);
    });

fetch('https://api.example.com/image')
    .then(response => {
        // 处理 Blob 响应
        return response.blob();
    })
    .then(blob => {
        const img = document.createElement('img');
        img.src = URL.createObjectURL(blob);
        document.body.appendChild(img);
    });

使用 Async/Await

async function fetchData() {
    try {
        const response = await fetch('https://api.example.com/data');
        if (!response.ok) {
            throw new Error('Network response was not ok');
        }
        const data = await response.json();
        console.log(data);
    } catch (error) {
        console.error('There has been a problem with your fetch operation:', error);
    }
}

fetchData();

错误处理

处理错误时，fetch 只会在网络故障或请求被阻止的情况下拒绝 Promise。对于 HTTP 错误状态码（如 404 或 500），需要手动检查响应的 ok 属性：

fetch('https://api.example.com/data')
    .then(response => {
        if (!response.ok) {
            throw new Error('HTTP error! status: ' + response.status);
        }
        return response.json();
    })
    .then(data => {
        console.log(data);
    })
    .catch(error => {
        console.error('There has been a problem with your fetch operation:', error);
    });

`fetch` 并行的异步请求

// 定义要获取的 URL 列表
const urls = [
    'https://api.example.com/data1',
    'https://api.example.com/data2',
    'https://api.example.com/data3'
];

// 使用 fetch 并行请求所有 URL
Promise.all(urls.map(url => fetch(url)))
    .then(responses => {
        // 检查所有响应是否都成功
        responses.forEach(response => {
            if (!response.ok) {
                throw new Error(`Network response was not ok for ${response.url}`);
            }
        });
        // 将所有响应解析为 JSON
        return Promise.all(responses.map(response => response.json()));
    })
    .then(dataArray => {
        // 处理所有解析后的数据
        console.log(dataArray);
    })
    .catch(error => {
        // 处理任何请求中的错误
        console.error('There has been a problem with your fetch operation:', error);
    });

Async/Await 进行并行请求

async function fetchDataInParallel(urls) {
    try {
        // 并行请求所有 URL
        const responses = await Promise.all(urls.map(url => fetch(url)));

        // 检查所有响应是否都成功
        responses.forEach(response => {
            if (!response.ok) {
                throw new Error(`Network response was not ok for ${response.url}`);
            }
        });

        // 将所有响应解析为 JSON
        const dataArray = await Promise.all(responses.map(response => response.json()));

        // 处理所有解析后的数据
        console.log(dataArray);
    } catch (error) {
        // 处理任何请求中的错误
        console.error('There has been a problem with your fetch operation:', error);
    }
}

// 定义要获取的 URL 列表
const urls = [
    'https://api.example.com/data1',
    'https://api.example.com/data2',
    'https://api.example.com/data3'
];

// 调用 fetchDataInParallel 函数
fetchDataInParallel(urls);