Monday, May 19, 2014

Downloading Javascript generated data

I have a number of web pages that generate some data in text areas using Javascript. The only way users could download this data was to copy and paste the contents of these text areas, but I wanted to add a download button to simplify the process. The problem is that this simply isn’t possible in Javascript. The only client-side solutions I’ve seen either require Flash or are not supported in all browsers.

So I came up with a slightly hacky and inefficient solution. The basic idea is to post the data to the server and get the server to return it to the client as a download. The HTML looks like this

      <form action="download.php" method="post">
          <input type="hidden" name="fileName" value="locations.csv" />
          <input type="submit" value="Download" />
        <textarea id="geocodedPostcodes" style="width:100%;" rows="20" name="data"></textarea>

All that is needed is a hidden field that tells the server-side script what the download file name should be and a text area with a name of “data”.

The server-side script is pretty simple, it looks like this

  header('Content-Disposition: attachment; filename="' . $_POST["fileName"] . '"');

  // add data

All it does is get the requested file name and echo back the data.

It’s seems a bit crazy (and a waste of bandwidth) that this seems to be the only way to achieve a seemingly simple task, but that looks to be the case. I’d be happy to be proved wrong.


Harry Oosterveen said...

Hello Chris,

You can actually create a downloadable file in Javascript using the data URI. See my example at

Chris Bell said...

That is a nice solution, but it doesn't seem to work in IE