'async' call in a function that does not support concurrency

Guri Bee

2 min read

·

22-10-2024

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The Illusion of Asynchronous: Using 'async' in Non-Concurrent Functions

Have you ever wondered why you might use the async keyword in a function that doesn't actually perform concurrent operations? This might seem counterintuitive, but it can be a powerful technique when dealing with I/O-bound tasks.

Let's explore this concept using a real-world example from the realm of web development. Imagine you're building a website that needs to fetch data from a remote API. You could use a simple function like this:

function fetchData(url) {
  return fetch(url)
    .then(response => response.json())
    .catch(error => console.error("Error fetching data:", error));
}

This function uses fetch to retrieve data from a given URL, parses it as JSON, and returns a promise that resolves with the data or rejects with an error. However, this function is synchronous. It blocks the execution of your code until the API response is received. This can lead to a laggy user experience if the API call takes a significant amount of time.

Enter the 'async' keyword. We can rewrite the above function using async to improve responsiveness:

async function fetchData(url) {
  try {
    const response = await fetch(url);
    return await response.json();
  } catch (error) {
    console.error("Error fetching data:", error);
  }
}

What's changed?

• The async keyword tells JavaScript that this function will return a promise.
• The await keyword pauses the execution of the function until the fetch call and the response.json() call are complete.

Why does this matter? Even though our function is not performing concurrent operations, using async allows us to handle the I/O-bound task (the API call) in a non-blocking way. This means that while waiting for the API response, the JavaScript engine can continue executing other tasks, like updating the UI or handling user interactions.

Let's look at a practical example:

async function displayData() {
  const data = await fetchData("https://api.example.com/data");
  document.getElementById("data-container").innerHTML = JSON.stringify(data);
}

// Trigger the function
displayData();

In this example, displayData calls fetchData using await, effectively pausing the execution of displayData until the data is fetched. However, the browser will still be responsive and can handle other user interactions during the wait time.

Key Takeaways:

• Using async in functions that don't perform concurrent operations allows for non-blocking I/O handling, improving responsiveness.
• async and await provide a cleaner and more readable way to work with promises compared to traditional callback functions.
• Remember to use try...catch blocks to handle potential errors during API calls.

Remember, even though your function isn't concurrent, using async can significantly enhance the user experience by preventing your code from being blocked while waiting for I/O operations to complete.

Attribution:

This article draws inspiration from discussions and examples found in GitHub repositories:

• https://github.com/facebook/react/issues/18857 - Discusses the use of async in React components for better code organization.
• https://github.com/nodejs/node/issues/3036 - Addresses the question of why async is used in non-concurrent scenarios.

Additional Resources:

• MDN Web Docs: async function
• MDN Web Docs: await

By understanding the benefits of using async even in non-concurrent scenarios, you can write more efficient and responsive JavaScript code, delivering a better experience for your users.