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Pavlovia: my jspsych experiment requires an external php file

URL of experiment:

Description of the problem:

I’ve coded my experiment in jspsych but provide external .json condition files for each participant. The problem here is that I need a way to reference a new file for every new participant. I figured a way to do this is to have a function that counts the number of files in the data folder and assigns file number based on that.

I.e.: (pseudocode)
subj_number = length(files in data)
condition_file = subject_file + subj_number + .json

From what I’ve gathered there’s no way of doing this directly using js code.
I’ve found a way to do this calling a .php script. And it works on my computer (on a local XAMPP server), however after I upload the whole experiment to Pavlovia if throws out an error reading the .php file :
Uncaught SyntaxError: Unexpected token <
I assume the issue is that Pavlovia doesn’t have a .php backend (but correct me if I’m wrong, I’m not very familiar with the topic).

So my question is, what is the easiest way around this issue? Can I somehow install php manually? Or can I write a python script that counts up the files and link it to the index.js file somehow? Or maybe there is another simpler solution?


P.S/ I’m not putting a link to URL, since currently uploaded version is working (since doesn’t include the .php call; I was making sure everything works fine)

We definitely can’t support you having a PHP script running on our server (security disaster). What PsychoPy/PsychoJS does is add a timestamp to data files so that they ensure no overwrites. Maybe you could do something similar? Adding a datestamp doesn’t require any PHP or interaction with the underlying filesystem (which is where the security issue comes in).

@apitiot might have an alternative solution for you

Hi Jon,

Thanks for the reply. From the way I see it, a timestamp would not solve the issue, because there is no way to bind the timestamp to a condition file unless I knew the timestamp in advance.

I.e. if I have a file named ‘participant3.json’, and a timestamp of when he started the experiment, there is still no way for the code to bind that file to that participant.

Oh, sorry, I mis-read. I thought you wanted to enforce unique data files but you want unique conditions files. Then I don’t have an easy solution for you. I guess you could interrogate the gitlab repository for the ( and count the files there using JS. Or you assign the participant number/condition as part of the URL in advance (so participant “3” is decided at recruit time rather than at start time)

This is basically what I was trying to do. The issue being that from what I found is there is no direct way of listing files using pure js. I could do it using either php code, node.js or through a python call somehow. Do you know if any of these methods is viable?

That’s a good idea, but I fear it might run into a similar issue: to know which participant is next (and which number to assign in the url), the code needs some kind of indication of how many participants already started the experiment