starting file download with JavaScript

Question

Let's say I have download links for files on my site.

When clicked these links send an AJAX request to the server which returns the URL with the location of the file.

What I want to do is direct the browser to download the file when the response gets back. Is there a portable way to do this?

Answer 1

We do it that way: First add this script.

<script type="text/javascript">
function populateIframe(id,path) 
{
    var ifrm = document.getElementById(id);
    ifrm.src = "download.php?path="+path;
}
</script>

Place this where you want the download button(here we use just a link):

<iframe id="frame1" style="display:none"></iframe>
<a href="javascript:populateIframe('frame1','<?php echo $path; ?>')">download</a>

The file 'download.php' (needs to be put on your server) simply contains:

<?php 
   header("Content-Type: application/octet-stream");
   header("Content-Disposition: attachment; filename=".$_GET['path']);
   readfile($_GET['path']);
?>

So when you click the link, the hidden iframe then gets/opens the sourcefile 'download.php'. With the path as get parameter. We think this is the best solution!

It should be noted that the PHP part of this solution is a simple demonstration and potentially very, very insecure. It allows the user to download any file, not just a pre-defined set. That means they could download parts of the source code of the site itself, possibly containing API credentials etc.