js实现异步处理

function fetchData(callback) {
    setTimeout(() => {
        const data = 'Hello, World!';
        callback(data);
    }, 1000);
}

fetchData((data) => {
    console.log(data); // 输出: Hello, World!
});

function fetchData() {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            const data = 'Hello, Promise!';
            resolve(data);
        }, 1000);
    });
}

fetchData().then(data => {
    console.log(data); // 输出: Hello, Promise!
});

function fetchData() {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            const data = 'Hello, async/await!';
            resolve(data);
        }, 1000);
    });
}

async function getData() {
    const data = await fetchData();
    console.log(data); // 输出: Hello, async/await!
}

getData();

async function getData() {
    try {
        const data = await fetchData();
        console.log(data);
    } catch (error) {
        console.error('Error fetching data:', error);
    }
}