Download csv file as response on AJAX request

I have an endpoint called '/downloadUserAction' that collects data and downloads a csv file. The challenge I am having is that the file won't get downloaded when calling endpoint using a button on click function, however it'll download only when I access the endpoint directly in the browser.

Upon research, I've came across findings that concluded that you cannot use AJAX to download files. That makes sense, since when I click on my button I see the endpoint being hit and the file contents being passed in the network tab, however no file gets downloaded on the client.

This is all I'm simply doing on the javascript side using data tables button plug-in feature on my page to call my endpoint.

$(document).ready(function () {
    var table = $("#userActivity").on('init.dt', function() {
            }).DataTable({
                dom: 'Blfrtip',
                buttons: [
                          {
                            extend: 'csvHtml5',
                            text: 'NLP Search Download',
                            action: function ( e, dt, node, config ) {
                                $.ajax({
                                    url : window.location + "/downloadUserAction?draw=3&search%5Bvalue%5D=NLP_SEARCH&order%5B0%5D%5Bcolumn%5D=6&order%5B0%5D%5Bdir%5D=desc"                        
                                });
                            }
                          }
                      ],

Is there another method of calling my endpoint that will force a download on the client page?

side-note: my data table is using server side processing otherwise I would've just used datatables csv exporting button.

Since it gets downloaded when you access the endpoint directly from the browser so what you can do is set an anchor tag inside the button and set the href attribute of the anchor tag to the url pointing to the csv file.I have created a sample example here:

<!DOCTYPE html>
<html>
<head>
    <title>Test</title>
</head>
<body>
    <button>
        <a href="http://www.sample-videos.com/csv/Sample-Spreadsheet-10-rows.csv">Click me</a>
    </button>
</body>
</html>

If you try out this code in browser, then onclick a dialog will appear for saving the file.

In your case you need the replace the sample videos url with your own.

window.location + "/downloadUserAction?draw=3&search%5Bvalue%5D=NLP_SEARCH&order%5B0%5D%5Bcolumn%5D=6&order%5B0%5D%5Bdir%5D=desc"

In modern browsers, you can prompt a download by creating a Blob with your file contents (in your case received by Ajax), creating a URL for it, and using the download attribute:

const saveData = (function () {
    const a = document.createElement("a");
    document.body.appendChild(a);
    a.style = "display: none";
    return function (data, fileName) {
        const blob = new Blob([data], {type: "octet/stream"}),
            url = window.URL.createObjectURL(blob);
        a.href = url;
        a.download = fileName;
        a.click();
        window.URL.revokeObjectURL(url);
    };
}());

const data = 'a,b,c\n5,6,7',
    fileName = "my-csv.csv";

saveData(data, fileName);

JSFiddle

If your Ajax endpoint URL has the proper headers (or possibly even if it isn't as long as you use the download attribute), you can forego the Blob and Ajax and just add the URL to the link with the download attribute. Adapting @pritesh's code,

const saveData = (function () {
    const a = document.createElement("a");
    document.body.appendChild(a);
    a.style = "display: none";
    return function (url, fileName) {
        a.href = url;
        a.download = fileName;
        a.click();
        window.URL.revokeObjectURL(url);
    };
}());

const url = 'http://www.sample-videos.com/csv/Sample-Spreadsheet-10-rows.csv', // Replace with your own URL: window.location + "/downloadUserAction?draw=3&search%5Bvalue%5D=NLP_SEARCH&order%5B0%5D%5Bcolumn%5D=6&order%5B0%5D%5Bdir%5D=desc"
    fileName = "my-csv.csv";

saveData(url, fileName);

JSFiddle