Using JavaScript Streams for Async Requests

Introduction to JavaScript Asynchronous Programming

Asynchronous programming in JavaScript is essential for handling concurrent operations effectively, improving code readability, and ensuring a seamless user experience. This tutorial covers streams, async/await, promises, iterators, and best practices for high-performance asynchronous workflows.

JavaScript’s Single-Threaded Nature

JavaScript runs on a single thread, meaning long operations block the main thread.

function longTask() {
  const end = Date.now() + 3000;
  while (Date.now() < end) {}
  console.log('Task complete');
}
console.log('Start');
longTask();
console.log('End');

This freezes the UI. To fix this, JavaScript uses the event loop + async programming.

Core Async Tools

Callbacks

function fetchData(cb) {
  setTimeout(() => cb('Data received'), 2000);
}
fetchData(console.log);

Callback hell makes this hard to maintain.

Promises

function fetchData() {
  return new Promise(resolve =>
    setTimeout(() => resolve('Data received'), 2000)
  );
}
fetchData().then(console.log);

Parallel tasks:

Promise.all([task1(), task2()]);

Async/Await

async function load() {
  const data = await fetchData();
  console.log(data);
}
load();

Parallel:

const [a,b] = await Promise.all([t1(), t2()]);

Streams & Async Iterators

Streams allow processing data chunk by chunk.

async function* streamData() {
  yield 'chunk 1';
  yield 'chunk 2';
}
for await (const part of streamData()) {
  console.log(part);
}

Use cases:

• reading large files
• network streaming
• paginated API batches

Conclusion

Mastering async tools—including streams, promises, and async iterators—helps developers build responsive, scalable applications.