Downloading large files with jQuery & iFrame - Need a File Ready event so I can hide the loading gif

Question

I'm using jQuery to download some files that take some time to create, so I show a loading gif to tell the user to be patient. But the problem is, the loading gif is currenntly shown and hidden all within a split second.

Is there a way for me to hide the loading gif after the download is complete and the user has the Save File popup on the screen?

HTML

<tr data-report_id="5">
    <td>
        <input type="button" id="donwload"></input>
        <img class="loading" src="/Images/Loading.gif"/>
        <iframe id="hiddenDownloader"></iframe>
    <td>
</tr>

JS

var reportId = $(this).closest("tr").attr("data-report_id");
var url = "/Reports/Download?reportId=" + reportId;

var hiddenIFrameId = 'hiddenDownloader';
var iframe = document.getElementById(hiddenIFrameId);
if (iframe === null) {
    iframe = document.createElement('iframe');
    iframe.id = hiddenIFrameId;
    iframe.style.display = 'none';
    document.body.appendChild(iframe);
}
iframe.src = url;
$(".loading").hide();

---

THE SOLUTION I ENDED UP USING

<script>
$("#download").on("CLICK", function () {
    var button = $(this);
    button.siblings(".loading").show();

    var rowNumber = GetReportId();
    var url = GetUrl();
    button.after('<iframe style="display:none;" src="' + url + '" onload="loadComplete(' + rowNumber + ')" />');
}

function loadComplete(rowNumber) {
    var row = $("tr[data-row_number=" + rowNumber + "]");
    row.find(".loading").hide();
}
</script>

<tr data-report_id="5">
    <td>
        <input type="button" id="download"></input>
        <img class="loading" src="/Images/Loading.gif" style="display:none;"/>
    <td>
</tr>

UPDATE

I was having problems with this method in Chrome so I changed all my jquery code to look for a cookie that the back end code set when the download had finished processing. When the jquery detected the cookie, it turned off the loading gif & whiteout.

Detect when browser receives file download

Answer 1

Have the iframe onload event call your code:

var reportId = $(this).closest("tr").attr("data-report_id");
var url = "/Reports/Download?reportId=" + reportId;

var hiddenIFrameId = 'hiddenDownloader';
var iframe = document.getElementById(hiddenIFrameId);
if (iframe === null) {
    iframe = document.createElement('iframe');
    iframe.id = hiddenIFrameId;
    iframe.style.display = 'none';
    iframe.onload = function() {
        $(".loading").hide();
    };
    document.body.appendChild(iframe);
}

iframe.src = url;