Suppose we have the following HTML file:
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Test iframe download</title>
<script type="text/javascript">
var init = 0;
function download() {
document.getElementById("dload_frame").src = "http://example.com/dload.py";
}
function alert() {
if (init == 0) {
init = 1;
}
else {
document.getElementById("alert_span").innerHTML = "Got it!";
}
}
</script>
</head>
<body>
<span id="alert_span">Main content.</span><br/>
<input type="button" value="Download" id="btn" onclick="download()" />
<iframe id="dload_frame" src="http://404.com/404" onload="alert()"> </iframe>
</body>
</html>
Now, if the URL to which iframe's src is being rewritten to (in this case - "http://example.com/dload.py") returns HTML, no problem: the onload event fires, the span's contents are replaced, everybody's happy.
However, if the content type of the file returned by the URL is set to something that forces the browser to open the save file dialog, the iframe's onload event never fires.
Is there any workaround? Using iframes isn't necessary, the desired behavior is to launch a callback after the browser begins downloading the supplied file.