How to Display a Progress Bar During Ajax Data Loading

When handling user-triggered events such as selecting values from a dropdown box, it's common to retrieve data asynchronously using Ajax. While the data is being fetched, it's beneficial to provide a visual indication to the user that something is happening. This article explores a method to display a progress bar during Ajax requests.

Implementing a Progress Bar with Ajax

To create a progress bar that accurately tracks the progress of an Ajax call, follow these steps:

1. Listen to Form Changes:

Utilize addEventListener('change') to listen for changes to the dropdown box.

2. Initiate Ajax Request:

Send an Ajax request to retrieve the desired data.

3. Using XMLHttpRequest for Progress Events:

In the Ajax options, configure the xhr function, which provides access to the XMLHttpRequest object. This object allows you to monitor various events, including progress.

4. Monitor Upload and Download Progress:

Within the xhr function, add event listeners to track both upload and download progress. These events include onloadstart, onprogress, and onloadend.

5. Update Progress Bar:

Use the progress event to calculate the percentage of progress based on the loaded and total properties of the event object, and update the progress bar accordingly.

Here's an example code snippet that demonstrates these steps:

$.ajax({
    xhr: function() {
        var xhr = new window.XMLHttpRequest();

        // Upload progress
        xhr.upload.addEventListener("progress", function(evt) {
            if (evt.lengthComputable) {
                var percentComplete = evt.loaded / evt.total;
                // Update progress bar...
            }
        }, false);

        // Download progress
        xhr.addEventListener("progress", function(evt) {
            if (evt.lengthComputable) {
                var percentComplete = evt.loaded / evt.total;
                // Update progress bar...
            }
        }, false);

        return xhr;
    },
    type: "POST",
    url: "/yourfile.php",
    data: "...",
    success: function(data) {
        // Handle successful data retrieval...
    }
});

By incorporating these techniques, you can effectively display a progress bar during Ajax data loading, ensuring a smooth and informative user experience.