Node.js — Async Programming

Callbacks

fs.readFile('file.txt', (err, data) => {
    if (err) throw err;
    console.log(data);
});

Promises

const readFile = (path) => {
    return new Promise((resolve, reject) => {
        fs.readFile(path, (err, data) => {
            if (err) reject(err);
            resolve(data);
        });
    });
};

readFile('file.txt')
    .then(data => console.log(data))
    .catch(err => console.error(err));

Async/Await

async function getData() {
    try {
        const data = await readFile('file.txt');
        console.log(data);
    } catch (err) {
        console.error(err);
    }
}

Promise.all

const results = await Promise.all([
    fetch('/api/users'),
    fetch('/api/posts'),
    fetch('/api/comments')
]);

Promise.race

const result = await Promise.race([
    fetch('/api/fast'),
    fetch('/api/slow')
]);

Mini Practice

1. Convert callbacks to promises
2. Use async/await
3. Parallel execution with Promise.all
4. Handle multiple promises

Up Next

Continue with Callbacks — callback patterns.