How do I return the response from an asynchronous call?

javascript

async-programming

promises

async-await

byNikita Barsukov·Feb 13, 2025

With async/await, you have a clean way of dealing with asynchronous operations. To craft a solution, make use of async functions, resembling synchronous code, but delivering asynchronous performance. await halts the function's execution until the Promise resolves:

async function getAsyncData(url) {
  try {
    const response = await fetch(url); // Just chilling while fetch complete 🍹
    return await response.json(); // And back on stage! Processing JSON response now 💃
  } catch (error) {
    console.error('Fetch error:', error);
  }
}

// Consumption of the async function
(async () => {
  const data = await getAsyncData('https://api.example.com/data');
  console.log('Received:', data); // Tada! 🎉 Here comes the fetched data
})(); // Let's roll 🚀

This method allows you to treat asynchronous responses similar to synchronous returns, while neatly managing errors with try/catch blocks.

Asynchronous JavaScript: The Basics

Dealing with async operations in JavaScript like $.ajax, fs.readFile, or fetch can be a bit befuddling at first. On firing an async operation, execution continues while the process is still ongoing and hence doesn't immediately return a value. Hence, callbacks, promises, or async/await are required to handle the results once ready.

Callbacks: The Fallen Heroes

Callbacks are the simplest way to handle async operations. They are essentially functions passed in as arguments that get executed once the async operation is done. It's like saying to JavaScript, "Hey JS, could you do this for me and give me a call(back) when you're done?" 😉:

// The async operation
setTimeout(() => console.log("Print after 1000ms."), 1000);

Callbacks have been around a while and were the pioneers of async handling, but notably can lead to what we call "callback hell", a tangled mess of callbacks within callbacks.

Promises: The New Age Solution

Promises allow a more elegant approach to dealing with asynchronous results. A Promise can be thought of as a placeholder for a value that would be eventually resolved.

const promiseWay = new Promise((resolve, reject) => {
  setTimeout(() => {
    resolve("Print after 1000ms."); // Promise, promise 🤞
  }, 1000);
});

promiseWay.then(console.log); // Who needs callback hell when you have Promises 🎊

async/await: The Crown Jewel

async/await are syntactic sugary toppings on the Promises. The await keyword makes JavaScript wait untill the Promise settles, while allowing other tasks to continue their execution.

async function asyncWay() {
  const response = await promiseWay;
  console.log(response); // Print after 1000ms.
}

asyncWay(); // An async way a day, keeps the callback hell away 🎉

Solutions to Common Pitfalls

Asynchronous programming is tricky and could step on the wrong tile. Here are few common traps:

Interchanging synchronous and asynchronous code

Confusing synchronous returns in asynchronous contexts could breed bugs. Understand where async code belongs and act accordingly.

Neglecting error handling

Errors can occur and overlooking them could lead to shaky promises and silent failures. Always remember to use catch() with Promises and try/catch with async/await.

Over-nesting callbacks

This leads to the infamous "callback hell". Instead of burying them into several layers, honor the callbacks to just one layer by using Promises or async/await.

Inefficient promise chaining

then() calls return new Promises which allows you to chain them. Learning how to perform several asynchronous operations in sequence effectively is a best practice.

Controlling Concurrency in Promises

JavaScript offers great help in controlling multiple asynchronous operations. Using Promise.all(), Promise.race() and Promise.allSettled() you can fine tune your async operations ensuring better efficiency, thus avoiding traffic jams in your app. 🚦🏎

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