JavaScript 异步编程：回调、Promise 与 async/await

回调地狱

fs.readFile('a.txt', (err, data1) => {

    fs.readFile('b.txt', (err, data2) => {

        fs.readFile('c.txt', (err, data3) => {

            // 多层嵌套，难以维护

        });

    });

});

Promise 链式调用

function readFilePromise(path) {

    return new Promise((resolve, reject) => {

        fs.readFile(path, 'utf8', (err, data) => {

            if (err) reject(err);

            else resolve(data);

        });

    });

}



readFilePromise('a.txt')

    .then(data => readFilePromise('b.txt'))

    .then(data => readFilePromise('c.txt'))

    .catch(err => console.error(err));

async/await（终极方案）

async function readAll() {

    try {

        const data1 = await readFilePromise('a.txt');

        const data2 = await readFilePromise('b.txt');

        const data3 = await readFilePromise('c.txt');

        return [data1, data2, data3];

    } catch (err) {

        console.error('读取失败:', err);

    }

}

并发执行

const [result1, result2] = await Promise.all([

    fetch(url1),

    fetch(url2)

]);

现代 JavaScript 异步编程首选 async/await，代码如同同步般清晰。