How Can I Achieve Asynchronous File Downloads in PHP?

Downloading Files Asynchronously with PHP: A Comprehensive Guide

When constructing interactive web applications, there often arises a need to download files asynchronously. This method allows you to retrieve files from a server without refreshing the entire page, improving user experience. This article focuses on utilizing PHP to achieve asynchronous file downloads.

We will delve into a common scenario where a button triggers an AJAX function. The AJAX function sends data to a PHP script, which in turn creates a CSV file based on the user's input. The challenge lies in prompting the browser to download this newly created CSV file.

AJAX Function for File Download Initiation

As outlined in the provided code snippet, the button click initiates the csv() AJAX function.

function csv(){
    $ajaxRequest = ajax();//ajax() initializes XML HTTP Requests
    $postdata = "data=" + document.getElementById("id").value;
    $ajaxRequest.onreadystatechange = function(){
        $ajaxDisplay = document.getElementById('ajaxDiv');
        if($ajaxRequest.readyState == 4 && $ajaxRequest.status==200){
            $ajaxDisplay.innerHTML = $ajaxRequest.responseText;
        }
    }
    $ajaxRequest.open("POST","csv.php",false);
    $ajaxRequest.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
    $ajaxRequest.send($postdata);
}

PHP Code for File Creation and Download Prompt

The csv.php script handles file creation and the download prompt. However, the provided script is not suitable for our purpose.

$fileName = 'file.csv';
$downloadFileName = 'newfile.csv';
if (file_exists($fileName)) {
    header('Content-Description: File Transfer');
    header('Content-Type: text/csv');
    header('Content-Disposition: attachment; filename='.$downloadFileName);
    ob_clean();
    flush();
    readfile($fileName);
    exit;
}
echo "done";

When this script is included at the end of csv.php, the contents of file.csv are displayed within the page (in the ajaxDiv element) rather than initiating a download.

Solution: Using a New Window for Download

To force a download, we cannot rely on AJAX. Instead, we can open a new window with the download link as its address or utilize document.location = ....

window.open('download.php?file=' . $fileName, '_blank');

// or

document.location = 'download.php?file=' . $fileName;

Conclusion

For asynchronous file downloads in PHP, avoid using AJAX. Consider opening a new window with the download link or redirecting the document's location to initiate the download.

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