PHP: Passing info to JavaScript

Question

say, my PHP script needs some time to calculate its operations. I need to keep the client informed about the operation progress. An example can be PHP based file download, where I need to provide to client estimated time needed to finish the download, and the amount of data that needs to be copied.

In PHP I can calculate all the needed information. However, how to regularly update the client with this info?

Ideally, I would like to dynamically update JavaScript variable from within my PHP script. I read that this is not possible, so what options do I have then?

Possibilities that come to my mind:

• Should I do regular AJAX calls from within my JavaScript into the PHP script to get the progress info?
• Should I study for me yet unknown COMET methodology

Do the two above possibilities make sense? Is there any other more practical solution available?

Thank you in advance.

Answer 1

Yes, both of those options make sense.

There are lots of different COMET-style techniques, but one of the simplest is a long-running iframe. You have a PHP page that monitors the progress of the operation, and outputs something like this at regular intervals:

<script>parent.updateProgress(relevantUpdateInfo);</script>

...where relevantUpdateInfo is the information about the progress, and updateProgress is a global function on the page containing the iframe that shows the updated information in the UI.

When outputting the script tags, be sure to flush the output.