Is onload equal to readyState==4 in XMLHttpRequest?

📝 Title: Understanding the Difference between onload and readyState==4 in XMLHttpRequest

👋 Hey there tech enthusiasts! Are you confused about the difference between onreadystatechange -> readyState == 4 and onload events in XMLHttpRequest? 🤔 Don't worry, you're not alone! In this blog post, we'll dive into this common question and provide easy solutions for better understanding. Let's get started! 💻

🔍 Background

The question revolves around the confusion between two methods of handling XMLHttpRequest events: onreadystatechange with the condition readyState == 4 and the onload event. To shed some light, let's look at the code snippet provided:

var xhr = new XMLHttpRequest();
xhr.open("GET", url, false);
xhr.onreadystatechange = function() {
    if (xhr.readyState === 4) {
        /* do something */
    }
};
xhr.send(null);

Alternatively, we have:

xhr.onload = function() {
    /* do something */
}

💡 Understanding the Concept

Both onreadystatechange and onload are event handlers used to perform actions when certain XMLHttpRequest events occur. However, there's a key difference between them.

🗝️ The Difference

• onreadystatechange is triggered multiple times during different stages of the XMLHttpRequest process, including when the status of the request changes. We need to explicitly check if the readyState property is 4 to ensure that the request is complete and the data is available for processing.

• On the other hand, onload is triggered only once, right after the request has been successfully completed. In this case, we don't need to check the readyState property explicitly.

🔧 Easy Solutions

If you're interested in performing actions as the readyState changes, you can use the onreadystatechange event as shown in the first code snippet. However, if you only want your code to execute once the request is complete, you can use the onload event as demonstrated in the second code snippet.

It's important to choose the right method based on your requirements. For example, if you need to update the UI as the request progresses, using onreadystatechange might be more suitable. On the other hand, if you only need to process the response when it's fully loaded, go for onload.

💡 Additional Tips

1️⃣ Remember to consider compatibility with different browsers. While both event handlers are widely supported, it's advisable to check the documentation for any specific nuances.

2️⃣ If your code requires making multiple requests, using onload might be more efficient as it ensures the request has truly completed.

📣 Take Action!

Now that you're equipped with this knowledge, go ahead and enhance your XMLHttpRequest implementation. Experiment with both onreadystatechange and onload to get a sense of which fits your needs better. Share your experiences and any additional tips in the comments below! Let's keep the conversation going and empower fellow developers. 🚀

🤓 That's a wrap, folks! We hope this guide has clarified the difference between onreadystatechange and onload in XMLHttpRequest for you. Stay tuned for more exciting tech contents, and don't forget to hit the share button to spread the knowledge! Till next time, happy coding! 💻💡✨