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Discover how to handle `asynchronous functions` in your Node.js application with WebSocket. Learn to send delayed responses in an efficient way.
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Calling an Asynchronous JavaScript Function on Server: A Complete Guide

Asynchronous programming is a powerful feature in JavaScript that allows for non-blocking operations. Imagine you have a webpage that communicates with a Node.js server using WebSocket. You've successfully implemented a synchronous response that sends data immediately after a request. But what if you want to introduce a delay before sending a response? This situation presents an interesting challenge, particularly when dealing with promises and async functions.

In this post, we'll break down the problem and explore how to effectively implement delayed responses on your server side using asynchronous JavaScript functions.

The Problem

You have a WebSocket connection between your client and server. Currently, when a specific message is sent from the client, the server responds instantly with a string. However, your goal is to create an asynchronous function that waits for a specified time (e.g., 4 seconds) before returning the response. The issue arises when you try to implement this – instead of the expected string, you receive "[object Promise]". Let's dive into what’s going wrong and how to fix it.

Current Implementation Overview

Here’s a simplified version of your current synchronous code:

[[See Video to Reveal this Text or Code Snippet]]

In order to introduce a delay, you've used the following setup involving asynchronous functions:

[[See Video to Reveal this Text or Code Snippet]]

Where Test invokes another method to get the result:

[[See Video to Reveal this Text or Code Snippet]]

Now, ShowResult and the asynchronous logic in GetAsync look like this:

[[See Video to Reveal this Text or Code Snippet]]

Understanding Promises and Async/Await

The main issue here is that the HandleASCIIMessage function is attempting to send the result of Test, which in turn resolves to a promise, not the actual string. Since async functions always return promises, your sz variable holds a promise rather than the resolved value.

How to Fix It

To resolve this, you need to make HandleASCIIMessage async and wait for the result before sending it back through the WebSocket. Here’s how you can implement this solution:

Update the Handle Method: Make HandleASCIIMessage an async function.

Await the Response: Use await to get the resolved value of Test() before sending the response.

Corrected Code Implementation

Here is how your updated HandleASCIIMessage should look:

[[See Video to Reveal this Text or Code Snippet]]

Now, when HandleASCIIMessage is called upon receiving a message, it will wait for the completion of Test, meaning ShowResult and subsequent functions, and only after the 4-second wait period, it will send the string "BANG" to the client.

Conclusion

Incorporating asynchronous functions on the server side can elevate your application by making it responsive while performing time-consuming operations. By understanding how promises and async/await work in JavaScript, you can effectively manage delayed responses without falling into common pitfalls like handling unresolved promises.

Feel free to implement this solution in your projects, and don’t hesitate to reach out if you have further questions or need assistance! Happy coding!