Asynchronous JavaScript and XML, or AJAX, is a web development technique used to create more dynamic and interactive web pages by allowing web pages to update information without needing a page reload. The jQuery library provides easy-to-use wrappers for the AJAX functionality, making it easy to add AJAX functionality to your web pages.
Downloading files through AJAX is a common use case which has been facilitated by JQuery with the help of its AJAX methods – the $.ajax(), $.get(), $.post() and $.getJSON().
In this article, we’ll take a look at how to use jQuery to download a file using AJAX, and provide step-by-step instructions to help you get started with your own project.
Asynchronous File Download using jQuery AJAX
In order to download a file asynchronously, we need to use the jQuery AJAX approach. Here's the basic outline for using AJAX to download a file:
$.ajax({
url: 'file/path/example.pdf',
method: 'GET',
xhrFields: {
responseType: 'blob'
},
success: function(blob,response,filename) {
var link=document.createElement('a');
link.href=window.URL.createObjectURL(blob);
link.download=filename;
link.click();
}
});
In the above code snippet, the url specifies the location of the file that we’re interested in downloading. The method property specifies that we want to use the HTTP GET method to retrieve the file.
The xhrFields property is used to set the responseType to blob. This indicates that we want the response to be treated as a binary Large Object (BLOB), which can be downloaded using a href attribute of an anchor tag.
In the 'success' function, we check that we have received a BLOB object and create a URL object from the resulting data blob with the help of window.URL.createObjectURL(blob). The link object is then used to simulate a click of a link to download the file with the help of link.download=filename; link.click();
In this example, we haven't passed any json data or headers such as space restrictions or other options. Tweak the above code accordingly according to your requirement.
jQuery AJAX File Download using POST Request
Sending POST Requests from AJAX can be done using jQuery AJAX() method as follows :
$.ajax({
type: "POST",
url: downloadURL,
data: JSON.stringify(data),
xhrFields: {
responseType: 'blob'
},
headers: {
'Content-Type': 'application/json'
},
success: function (response, status, xhr) {
var filename = "";
var disposition = xhr.getResponseHeader('Content-Disposition');
if (disposition) {
var filenameMatch = disposition.match(/filename[^;=
]*=((['"]).*?\2|[^;
]*)/);
if (filenameMatch != null && filenameMatch[1]) {
filename = filenameMatch[1].replace(/['"]/g, '');
}
}
var type = xhr.getResponseHeader('Content-Type');
var blob = new Blob([response], { type: type });
var URL = window.URL || window.webkitURL;
var downloadUrl = URL.createObjectURL(blob);
if (filename) {
// use HTML5 a[download] attribute to specify filename
var a = document.createElement("a");
// safari doesn't support this yet
if (typeof a.download === 'undefined') {
window.location.href = downloadUrl;
} else {
a.href = downloadUrl;
a.download = filename;
document.body.appendChild(a);
a.click();
}
} else {
window.location.href = downloadUrl;
}
},
error: function (xhr, message, errorThrown) {
console.log('Error when downloading file', errorThrown);
console.log('HTTP status:', xhr.status);
}
});
The change in this block of code comes from the fact that we have passed JSON data in the 'data' property. When downloading files using POST requests, passing Binary data using fetch API endpoint as a data blob is not possible. Hence we’re passing JSON data which can be parsed by an endpoint or server-side code. The server will then send the file back to the client, which we’ll then be able to download via the responseType property.
jQuery File Download with Progress Bar
Using jQuery, we can also create a progress bar to indicate the status of the file download. Here’s how you can add a progress bar to your file download process:
var downloadXhr = new XMLHttpRequest();
downloadXhr.withCredentials = true;
downloadXhr.open('GET', fileUrlPath, true);
downloadXhr.responseType = 'blob';
downloadXhr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
downloadXhr.addEventListener("progress", updateProgress, false);
downloadXhr.onreadystatechange = function () {
if (downloadXhr.readyState == 4 && downloadXhr.status == 200) {
var blob = downloadXhr.response;
var link = document.createElement("a");
link.href = URL.createObjectURL(blob);
link.download = filename;
document.body.appendChild(link);
link.dispatchEvent(new MouseEvent('click'));
document.body.removeChild(link);
updateProgress({ loaded: 100, total: 100 });
}
};
downloadXhr.send();
function updateProgress(evt) {
if (evt.lengthComputable) {
// calculate percentage
var percentComplete = evt.loaded / evt.total;
percentComplete = parseInt(percentComplete * 100);
// show progress
console.log(percentComplete);
}
}
Here, we define an XMLHttpRequest object for the download and specify the URL that we’re interested in downloading. We also set the Content-Type header to “application/x-www-form-urlencoded” to make sure that the data download is in the correct format.
We also set the withCredentials property to true to send authentication information along with the file download requests. After that, we register an event listener to update the progress of the file download process.
Once the file has been successfully downloaded, we create a link to the file and simulate a click event to download the file.
We also define an updateProgress() function to update the progress bar, using the loaded and total arguments of the progress event.
Conclusion
In this article, we have discussed various ways in which you can use jQuery AJAX to download files from the server-side. We have seen how to use GET and POST Request Method and how dataType: "blob" can be used to download binary data.
We have also seen how to implement a progress bar to indicate the status of the file transfer in real-time.
There is a lot more you can do with AJAX file downloads in jQuery, and this article provides just a starting point. So put these concepts into practice and enjoy the benefits of making your web pages more interactive and dynamic.
let’s dive a bit deeper into each topic covered in the article on jQuery AJAX file downloads.
Asynchronous File Download using jQuery AJAX
The code example provided shows a basic implementation of downloading a file using AJAX. While it’s a straightforward process, it’s important to handle error cases. For instance, if the file isn’t accessible or the network connection is lost, the application should handle these errors and communicate them to the user.
Another important aspect to consider is the security implications of file downloads. If you’re downloading files from sources that aren’t trusted, you should validate that the response type is indeed a blob object and that it’s not something malicious. You should always sanitize and validate user input to avoid any attacks like SQL injection or Cross-Site Scripting (XSS).
jQuery AJAX File Download using POST Request
When downloading files using POST requests, you have to be mindful of the size of the payload that you’re sending. Typically, HTTP POST has the maximum allowed payload size, which ranges from a few kilobytes to a few megabytes depending on the server.
The example code used JSON data, but you can use any other type of data to send in the body. It’s essential to make sure that the server-side code handles the data as expected and responds with the correct content type to allow the file to be downloaded correctly.
jQuery File Download with Progress Bar
Implementing a progress bar is a good way to keep the user informed about the stage of the download process. It tells the user how much longer they have to wait before they can access the file.
The progress bar is particularly useful for larger files since they take longer to download. It’s also essential to handle the scenario where the download process is interrupted. Interrupting the download process can happen due to various reasons such as a network interruption, user intervention, or server failure. In such scenarios, the user should be informed of what happened and prompted to try again.
Final Thoughts
jQuery AJAX is a powerful library that simplifies the process of asynchronous requests and responses to and from a server. XMLHttpRequests and response handling functionality provided by jQuery AJAX make downloading files from a web server a straightforward and streamlined process.
When implementing any file download processes, it's vital to follow best practices to avoid security concerns and error handling scenarios. Downloading files asynchronously can improve the user experience greatly, making web pages feel more dynamic and responsive. The versatility and flexibility of jQuery AJAX make it an essential tool for web developers who want to create modern and responsive web applications.
Popular questions
- What is jQuery AJAX?
jQuery AJAX is a method for retrieving data from a web server without requiring a full page reload. It allows web developers to update parts of a web page in response to user actions, without reloading the entire page.
- How can we download a file using jQuery AJAX?
To download a file using jQuery AJAX, we can use the $.ajax() method and specify the URL of the file we want to download. We can also use the xhrFields property to specify the response type as a binary Large Object (BLOB), which we can then download using an anchor tag.
- How can we download files using POST requests with jQuery AJAX?
We can download files using POST requests by using the $.ajax() method and specifying the HTTP method as POST. We can also pass JSON data using the data parameter, which the server-side code can parse to retrieve the file to download.
- What is a progress bar, and how can we implement it when downloading files using jQuery AJAX?
A progress bar is an element that shows the progress of a file download or upload. It’s meant to help users visualize how much longer they have to wait before they can access the file. We can implement a progress bar when downloading files using jQuery AJAX by registering an event listener that updates the progress bar as the download progresses.
- Is it important to handle potential errors when downloading files using jQuery AJAX?
Yes, it is important to handle potential errors, such as network interruptions or file unavailability when downloading files using jQuery AJAX. Proper error handling can help improve user experience and prevent malicious attacks against the application. Adequate error handling should communicate errors to the user and prompt them to try again or take some other action.
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